Cfje ftural Cext=2froofe ^crteg 

Edited by L. H. Bailey 



THE 

PRINCIPLES OF IRRIGATION 

PRACTICE 



Cfje ftural Cext=2?ook ^erte* 

Edited by L. H. BAILEY 



Mann, Beginnings in Agriculture 

Warren, Elements of Agriculture 

Warren, Farm Management 

Lyon and Fippin, Soil Management 

J. F. Duggar, Southern Field Crops 

B. M. Duggar, Plant Physiology 

Harper, Animal Husbandry for Schools 

Montgomery, The Corn Crops. 

Wheeler, Manures and Fertilizers 

Livingston, Field Crop Production 

Widtsoe, Principles of Irrigation Practice 



Others in Preparation 




Brigham Young. (Born 1801; died 1877 J 
The founder of modern irrigation in America. 



THE PRINCIPLES OF , 

IRRIGATION PRACTICE 



BY 



JOHN A. WTDTSOE, A.M., Ph.D. 

President of the Utah Agricultural College 



J&tto gorfe 
THE MACMILLAN COMPANY 

LONDON: MACMILLAN & CO., Ltd. 
1914 

AU rights reserved 






Copyright, 1914 
By THE MACMILLAN COMPANY 



Set up and electrotyped. Published August, 1914 



Mount pleasant i^rtss 

J. Horace McFarland Company 
Harrisburg, Pa. 

AUG 27 1914 

©CI.A38011!) 



too 



/ 



BY THE AUTHOR TO THE MEMORY OF THE 
PIONEERS WHO, ON JULY 24, 1847, ENTERED THE 
GREAT SALT LAKE VALLEY, AND ON THAT DAY 
FOUNDED MODERN IRRIGATION IN AMERICA 



PREFACE 

Irrigation and dry-farming are rapidly conquering 
drought. By these twin arts, bountiful and regular 
harvests may be gathered in the humid regions during 
the periodic dry seasons; and in the arid regions, the 
great "deserts" may be converted into most fruitful fields. 
Irrigation has a splendid record of success from the begin- 
ning of history; dry-farming has only in recent days 
extended its conquests into the more arid regions; both 
have become more powerful in conquering drought as 
modern science has been applied to them. 

Successful irrigation-farming is the joint product of 
the engineer and the farmer. To the engineer is given the 
heavy and responsible task of constructing properly a 
permanent system of dams and canals from which water 
may be drawn; to the farmer belongs the apparently 
humble but unending and difficult task of using the 
water in the best manner for crop-production. Both 
workers are essential for success; but, the work of the 
farmer determines the permanence and extent of agricul- 
ture under irrigation. 

Much has been written about irrigation for the 
engineer, but little for the farmer. The few who have 
written about farming under irrigation have, most fre- 
quently, prepared crop or soil manuals, in which the use 
of water has formed a minor part. This book is an attempt 
to develop the principles, so far as present knowledge per- 
mits, upon which the correct use of water, by the farmer, 

(ix) 



X PREFACE 

must rest. Crop or soil treatments which are not con- 
nected directly with the use of water are not discussed or 
are greatly subordinated. The various aspects of the 
complex art of irrigation — agricultural, economic, social 
and legal — will some day receive separate and special 
treatment; in this volume one line of thought only has 
been followed — the correct use of water in irrigation. 

The aim of this book is to furnish to students and 
intelligent farmers a modern view of the principles of 
irrigation practice. Simple language has been used and 
unnecessary technical terms have been avoided. Obvious 
matters, and those which vary with local conditions and 
must therefore be learned by experience, have been 
eliminated. The beginner in irrigation has been kept in 
mind; but the book is essentially a manual for those who, 
whether in arid or humid climates, having cast their lots 
with irrigation, desire mastery of their work by an intel- 
ligent comprehension of the natural laws involved in 
irrigation-farming. The actual handling of water can be 
learned only by experience — that is the beginner's heavy 
lesson; the refinements of irrigation, by which its success 
at last is measured, come later, and are unknown to 
many. The man who lives year after year under the 
ditch, and raises his family there, needs as much if not 
more help than the pioneer whose chief sorrow is the 
aggravating self-will of the water as it flows over the 
newly broken land. 

Some subjects have been touched on lightly in this 
volume because they are more fully developed in the 
author's book on "Dry-Farming." In fact, that book 
and this one are a continued study of the water factor in 
agriculture — perhaps the most important of the physical 
factors. Schools of agriculture, whether in arid or humid 



PREFACE xi 

regions, might profitably organize classes in this subject. 
Classes in fertilizers and related subjects are taught as 
a matter of course, but the water factor, of greater impor- 
tance, is given incidental mention in courses on soils or 
plant physiology. At the Utah Agricultural College it has 
been found satisfactory to give a half-year course in dry- 
farming, followed by a half-year course in irrigation 
practice, the two courses constituting a year's study of 
the water factor in agriculture. 

The irrigation literature of the world has been quite 
fully examined in the preparation of this book; but, since 
the work has been done far from large libraries, many 
important papers have been inaccessible. However, as a 
possible compensating condition, the work has been done 
within hearing of the ripple of the irrigation ditch, in 
the heart of the irrigated section. Free use has been made 
of all available information, but of especial help have 
been the magnificent series of irrigation bulletins issued 
by the Irrigation Investigations of the Office of Experi- 
ment Stations of the United States Department of Agri- 
culture. The splendid work of the Bureau of Soils of the 
United States Department of Agriculture has also been 
of the greatest assistance. It is a pity that the heated dis- 
cussion of a theory should overshadow this vast, accurate 
and remarkable soil work, the like of which, issuing from 
one institution, is not to be found. 

At the end of each chapter has been placed a short 
list of references for the use of those who desire to carry 
their studies further. Care has been taken, except in 
two or three instances, to suggest only such materials as 
are readily available. These references would make a 
very good working library on irrigation and may be 
obtained at a slight cost. In Appendix C is given a brief 



xii PREFACE 

list of books on irrigation. No attempt is made to supply- 
in this volume a complete bibliography of irrigation. 

To friends and colleagues in many parts of the world 
hearty thanks are offered for valuable help rendered in 
the preparation of this book. My Utah colleagues, many 
of whom have been connected with the long experimental 
study of irrigation at the Utah Station, have given freely 
of their time and information to make the book accurate 
and worthy of the cause. I am under particular obliga- 
tion to Dr. Robert Stewart, Dr. F. S. Harris, Prof. W. W. 
McLaughlin and Prof. L. A. Merrill, and to Librarian 
Elizabeth C. Smith, who has kindly gathered irrigation 
literature from all parts of the world. My brother, Prof. 
O. J. P. Widtsoe, has in many ways given most valuable 
help. If this book and its companion volume shall be of 
service, the first credit belongs to Dr. L. H. Bailey, the 
Editor of the Rural Series of books, through whose wise 
and kindly urging these books were written, and the many 
others, by other hands, which have made available to 
humanity the great applications of modern science to 
rural problems. 

JOHN A. WIDTSOE. 

Logan, Utah. 



NOTE. — Unless otherwise stated, wherever 
4 'inch" or "foot" of water is used in this book 
it refers to the depth to which the water would 
cover the ground. 



TABLE OF CONTENTS 

A. INTRODUCTION 

CHAPTER I 

Pages 

The Meaning of Irrigation 1-7 

Annual rainfall, 1 — Seasonal rainfall, 2 — Variations in 
rainfall, 2 — Conservation of rainfall on farms, 3 — Condi- 
tions of dry-farming, 3 — Conditions of irrigation, 4 — 
Irrigation defined, 4 — Geographical need of irrigation, 5 
— Possible extent of irrigation, 5 — Mission of irrigation 
and dry-farming, 7. 

B. THE RELATION OF WATER TO SOILS 

CHAPTER II 

Soil Moisture 8-20 

Attraction between near bodies, 8 — Soil particles, 9 — 
The soil-moisture film, 11 — Thickness of film and diame- 
ter of particles, 12 — Hygroscopic coefficient, 13 — The 
wilting coefficient, 14 — Lento-capillary point, 16 — 
Maximum capillary capacity, 17 — Free water, 17 — 
Summary, 19. 

CHAPTER III 

The Soil as Water Reservoir 21-39 

Irrigated soils are unsaturated, 22 — The movement of soil 
moisture, 23 — The distribution of soil moisture, 25 — 
Field moisture capacity, 29 — Water distribution in 
furrow irrigation, 30 — Effect of hardpan, 32 — Effect of 
gravel, 34 — Water table near surface, 34 — Soil treatment, 
35 — How much water can be stored, 35 — Absorption of 
water by soils, 38. 

(xiii) 



xiv TABLE OF CONTENTS 

CHAPTER IV 

Pages 

Saving Water by Cultivation 40-63 

The run-off, 40 — The upward movement of water, 42 — 
Intensity of evaporation, 44 — Conditions determining 
evaporation, 46 — Mulching to check evaporation, 49 — 
Self-mulching soils, 52 — Time of cultivation, 53 — 
Depth of cultivation, 55 — Frequency of cultivation, 58 — 
Cultivation and soil fertility, 59 — Rolling, 62. 

CHAPTER V 

Soil Changes Due to Irrigation Water .... 64-107 

Contraction and moisture film, 64 — Cohesion of soil 
particles, 65 — Volume changes of soils, 67 — Effect on top 
soil, 69 — Successive wetting and drying, 70 — Natural 
packing of soil, 70 — Soil temperature, 71 — Water a 
universal solvent, 72 — Humid and arid soils contrasted, 
73 — Continuous solubility of soils, 74 — Absorption by 
soils, 76 — Composition of drainage water, 78 — Concen- 
tration of soil moisture, 79 — Loss by drainage, 79 — 
Upward leaching, 81 — Salinity of river waters, 82 — 
Salinity of lake waters, 86 — Salinity of mineral springs, 
86 — Soil moisture and natural waters compared, 87 — 
Ash constitutents added by irrigation water, 87 — Use of 
concentrated waters, 89 — Need of water surveys, 90 — 
Composition of natural waters, 90 — Classification of 
natural waters, 92 — Plant-food value of irrigation 
water, 93 — Suspended matter in river water, 95 — Sea- 
sonal variation of suspended matter, 98 — Suspended 
matter added to soil by irrigation, 100 — Suspended 
matter derived from surface soils, 100 — Composition of 
river sediments, 101 — Physical effects of sediments, 
102 — Cultural treatment of sediments, 103 — Effect of 
sediments on crop-yields, 104 — Water and soil life, 
104. 



TABLE OF CONTENTS XV 

C. THE RELATION OF WATER TO PLANTS 

CHAPTER VI 

Pages 

Conditions Determining the Use of Soil Moisture by 

Plants 108-126 

Absorption of water by roots, 109 — Transpiration, 110 — 
The initial percentage of soil moisture, 111 — Distribution 
of water in the soil, 114 — The effect of time, 115 — The 
depth of soil, 116 — Physical composition of soils, 117 — 
Chemical compositions of soils, 118 — Plowing, 120 — 
Cultivation, 121 — Manuring, 121 — Vigor of plant, 121 — 
Root-system, 122 — Age of plants, 122 — The kind of crop, 
123— The seasons, 124. 

CHAPTER VII 

The Water-Cost of Dry Matter 127-157 

Carbon-assimilation, 128 — Plant age and carbon-assimi- 
lation, 129 — Conditions of growth, 130 — The transpira- 
tion ratio, 131 — The seasons, 136 — The soil, 137 — 
Mineral food or soil fertility, 139 — Cultural operations, 
141 — The vigor of the plant, 143 — Varying quantities 
of water, 144 — Maximum yield with given quantity of 
water, 151 — The nature of the crop, 154 — Summary, 155. 

CHAPTER VIII 

Crop Development Under Irrigation 158-172 

Response to irrigation, 159 — Proportion of roots, 160 — 
Proportion of leaves and stems, 163 — Proportion of heads 
and grain, 166 — Other plant parts, 169. 



xvi TABLE OF CONTENTS 

CHAPTER IX 

Pages 

The Time of Irrigation 173-188 

The ideal principle, 173 — Fall irrigation, 175 — Winter 
irrigation, 178 — Early spring irrigation, 181 — Irrigation 
during growth, 182 — Time of irrigating short-season 
crops, 183 — Time of irrigating long-season crops, 184 — 
Night versus day irrigation, 187. 

CHAPTER X 

The Method of Irrigation 189-215 

Sub-surface irrigation, 189 — Surface irrigation, 193 — 
Permanent ditches, 196 — Field-ditch or field-lateral 
method, 198— The border method, 202— The check 
method, 202— The basin method, 207— The furrow 
method, 207 — Summary, 214. 

CHAPTER XI 

Crop Composition 216-230 

Groups of plant constituents, 217 — Water, 217 — Ash, 
219— Protein, 220— Fat, 223— Carbohydrates, 224— 
Sugars, 224— Starch, 226— Woodiness, 226— Color and 
flavor, 227— Flour, 227— Cooking value, 228— Effect 
of cultural treatment, 228. 

D. CROPS UNDER IRRIGATION 

CHAPTER XII 

The Use of the Rainfall 231-239 

Irrigation supplementary to rainfall, 231 — Crop-pro- 
ducing power of rainfall, 232 — Results of dry-farming, 
233 — Crop value of rainfall in irrigation, 233 — Conserv- 
ing the rainfall, 235- — Distribution of rainfall, 235 — 
Storing water in the soil, 236 — Cultivation, 237 — Pro- 
portion of rainfall conserved, 237 — Relation of irriga- 
tion and dry-farming, 237 — Dry-farm homesteads, 238. 



TABLE OF CONTENTS xvil 

CHAPTER XIII 

Pages 

Irrigation of Cereals 240-265 

Spring vs. fall wheat, 241 — Quantity of wheat to sow, 
241 — Method of sowing wheat, 242 — Cultivation of 
wheat, 243 — Method of irrigating wheat, 243 — Time to 
irrigate wheat, 246 — Quantity of water for wheat, 248 — 
Oats, 253— Barley, 255— Rye, 255— Corn, 255— Time 
to irrigate corn, 258 — Quantity of water for corn, 259 — 
Rice, 262. 

CHAPTER XIV 

Alfalfa and Other Forage Crops and Pastures 266-285 

Alfalfa or lucern, 266 — Cultivation of alfalfa, 268 — 
Method of irrigating alfalfa, 269 — Time to irrigate alfalfa, 
270 — Quantity of water for alfalfa, 274 — Alfalfa seed, 277 
— Hay-making crops, 278 — Red clover, 281 — Pastures 
and meadows, 281. 

CHAPTER XV 

Sugar Beets, Potatoes and Miscellaneous Crops . 286-313 
Sugar beets, 286 — Method of irrigating sugar beets, 289 
— Time to irrigate sugar beets, 290 — Quantity of water 
for beets, 293— Carrots, 296— Other root crops, 297— 
Potatoes, 298 — Peas and beans, 301 — Fiber crops, 305 — 
Hops, 306 — Tomatoes, cantaloupes, etc., 306 — Cab- 
bage, cauliflower, etc., 308 — Asparagus and celery, 309 — 
Onions and miscellaneous crops, 310. 

CHAPTER XVI 

Fruit Trees, Other Trees and Shrubs .... 314-330 
Fruit-growing, 314 — Method of orchard irrigation, 315 — 
Time of orchard irrigation, 319 — Quantity of water for 
orchards, 322 — Other conditions of orchard irrigation, 
323— Nursery stock, 326— Small fruits, 326— Grape- 
vines, 327 — Plants for ornament and comfort, 328. 



xviii TABLE OF CONTENTS 

E. MISCELLANEOUS 
CHAPTER XVII 

Pages 

The Duty, Measurement and Division of Water . 331-370 

The duty of water, 331 — Classes of duty, 334 — Deter- 
mination of duty of water, difficult, 336 — Duty of water 
in Africa, 338 — Duty of water in Asia, 339 — Duty of 
water in Europe, 341 — Duty of water in South America, 
342 — Duty of water in Australia, 343 — Duty of water in 
North America, 343 — Bear River Canal experience, 344 — 
Idaho results, 345 — Miscellaneous results, 345 — The 
Utah results, 346 — Need of measuring water, 347 — Who 
shall measure the water? 349 — Classes of measurement, 
349— The Cippoletti weir, 353— Divisors, 355— Mean- 
ing of the distribution of water, 357 — Methods of Dis- 
tribution, 358 — Continuous flow, 358 — Continuous 
rotation, 361 — Distribution on application, 364 — Organi- 
zation for distribution, 365 — Regulations and records, 
368. 

CHAPTER XVIII 

Over-Irrigation and Alkali 371-405 

Seepage from reservoirs and canals, 371 — Loss from 
excessive irrigation, 373 — Ground water, 374 — Com- 
parison with humid areas, 375 — Lined ditches — a rem- 
edy, 376 — The economical use of water — a remedy, 381 — 
Drainage — the final remedy, 381 — Alkali defined, 383 — 
Seepage and alkali, 384 — Upward leaching, 385 — Use of 
saline water, 387 — Alkali deposits, 388 — Kinds of alkali, 
390 — Tolerance for alkali, 392 — Cropping against 
alkali, 397 — Chemical treatment for alkali, 398 — Scra- 
ping the surface, 399 — Tillage against alkali, 399 — Wash- 
ing out alkali, 400 — Underdrainage — the final remedy, 
400. 



TABLE OF CONTENTS xix 

CHAPTER XIX 

Pages 

Irrigation in Humid Climates 406-418 

Dry seasons, 407 — Results of irrigation in humid 
regions, 409 — Methods of applying water, 412 — The duty 
of water, 413 — Sources of water, 413 — Water-conserva- 
tion methods, 414 — Value of sewage water, 414 — The 
use of sewage, 415 — Factory and mill waste, 417. 

CHAPTER XX 

Irrigation Tools and Devices 419-444 

Clearing and breaking the land, 419 — Laying-out the 
farm, 420 — Leveling the land, 423 — Making farm 
ditches, 426 — Gates and checks, 434 — Ridging and fur- 
rowing, 439 — Mulching the soil, 440 — Measuring the flow 
of water, 441. 

CHAPTER XXI 

The History of Irrigation 445-471 

The antiquity of irrigation, 445 — The Christian era to 
1800, 449 — Irrigation in recent times, 451 — The found- 
ing of modern irrigation in America, 454 — The growth of 
American irrigation, 457 — The Union Colony of Colorado, 
460 — The United States Reclamation Service, 461 — 
The United States Department of Agriculture, 464 — 
The experiment stations, 466 — The Irrigation Con- 
gress, 470. 

CHAPTER XXII 

Permanent Agriculture under Irrigation . . . 472-476 
The big irrigation problem, 472 — The spirit of irrigation, 
473 — No essential difference between irrigation- and 
humid-farming, 473 — History assures permanence of 
irrigation, 474 — The question of plant-food, 474 — Some 
advantages of irrigation, 476 — Finally, 476. 



xx TABLE OF CONTENTS 

APPENDIX 

Pages 

A. Water Constants 477 

B. Discharge over Cippoletti's Weir 478-483 

C. List of American Books on Irrigation . . . 484 

INDEX 485-496 



LIST OF ILLUSTRATIONS 

Fig. Page 

Brigham Young Frontispiece 

1. Progressive averages of annual rainfall 3 

2. The limited water supply makes it unlikely that more than one- 

tenth of the land will be irrigated 5 

3. The value of water in an arid land 6 

4. Soil is a mixture of particles of very varying size 10 

5. The moisture film surrounding a soil particle 18 

6. Flooding new land 24 

7. Distribution of water in soil immediately after an irrigation .... 27 

8. Distribution of water in soil under furrow irrigation 31 

9. Penetration of roots of prune tree 36 

10. Evaporation usually exceeds rainfall 44 

11. Relation between temperature and evaporation 48 

12. Evaporation losses from soils protected with mulches of differ- 

ent depths 51 

13. Orchard well cultivated to prevent evaporation 57 

14. Mulching the garden with a hand cultivator 61 

15. Adhesion of hairs due to water 65 

16. Cracked river sediments showing volume changes due to water 68 

17. Midsummer snow in the tops of the mountains 75 

18. Badly corroded ditch due to excessive fall 95 

19. Walled ditch to prevent erosion of easily "washed" soil 97 

20. Daily discharge of Malheur River 99 

21. Daily discarge of Mackenzie River 99 

22. Deposit in field of suspended matter from irrigation water 102 

23. Stomatal apparatus in carnation leaf 132 

24. Determining the transpiration ratio 135 

25. Yield of dry matter of cereals with varying quantities of water . . 149 

26. Yield of dry matter of cereals per inch of irrigation water 149 

27. Crop-producing power of 30 acre-inches (wheat) 152 

28. Crop-producing power of 30 acre-inches (alfalfa) 152 

29. Crop-producing power of 30 acre-inches (sugar beets) 153 

30. Effect of little, medium and much water on wheat 160 

31. Proportion of grain and straw with varying irrigations 168 

32. Plan of a sub-irrigated farm 191 

33. Lee's sub-irrigation system 192 

(xxi) 



xxii LIST OF ILLUSTRATIONS 

Fig. Page 

34. A permanent ditch in an orange grove 196 

35. Plan of field-ditch irrigation 197 

36. Flooding from ditches running down the steepest slope 198 

37. Flooding from field ditch 198 

38. Flooding with aid of canvas dam 199 

39. Laterals made in field and dammed with small piles of manure 

for next year's irrigation 200 

40. Plan for border irrigation 201 

41. Border method of irrigation 202 

42. Irrigating cherries under check system 203 

43. Rectangular check method of irrigation 204 

44. Contour check method of irrigation 205 

45. Filling checks with detachable pipes .• 206 

46. Orchard irrigation by basin method 207 

47. Orchard irrigation by basin method 207 

48. Grading of interior of basins to prevent water from coming in 

contact with trees 208 

49. Furrow irrigation 208 

50. Furrow irrigation of young alfalfa 209 

51. One-way furrow irrigation 210 

52. Furrowing land 211 

53. Standpipe supplying furrows with water 212 

54. Zigzag furrows to insure uniform distribution over soil 213 

55. Another type of zigzag furrows 214 

56. Lath-box for distributing water to furrows from head ditch. . . . 214 

57. Yield of crops due to rainfall 235 

58. Irrigating wheat 244 

59. Canvas dam to check water 245 

60. Irrigated wheat 249 

61. Irrigated oats 251 

62. Plan of rice irrigation 254 

63. Yield vs. water (wheat) 256 

64. Producing power of 30 acre-inches 257 

65. Yield vs. water (corn) 261 

66. Irrigated corn in Arizona 262 

67. Plan of irrigating an alfalfa field 270 

68. Temporary county fair building constructed of baled alfalfa hay 271 

69. An alfalfa field in Nevada 272 

70. Yield vs. water (alfalfa) 276 

71. Flooding pasture land 280 

72. Irrigating young alfalfa 281 

73. Irrigated cane in Kansas 283 

74. A sugar beet field 287 



LIST OF ILLUSTRATIONS xxiii 

Fig. Page 

75. Loading sugar beets in factory bins 288 

76. Irrigating potatoes 293 

77. Yield vs. water (sugar beets) 295 

78. Plan of potato irrigation 298 

79. Irrigating potatoes 299 

80. Irrigated field peas 302 

81. Irrigated celery 304 

82. Irrigated pumpkins 305 

83. Irrigated onions 307 

84. Yield vs. water (potatoes) 309 

85. Irrigated Egyptian cotton 311 

86. Irrigating cantaloupes 312 

87. Irrigating an apple orchard 318 

88. On the upper canal 322 

89. An irrigated prune orchard 325 

90. An irrigated date palm orchard 328 

91. Canal crossing river in an inverted syphon 332 

92. Looking down the Bear River Canal 333 

93. Lateral outtake from large canal 335 

94. Headgate of a canal 340 

95. A cable measuring station with automatic gauge 348 

96. Lyman rectangular weir 350 

97. Longitudinal section of Lyman's weir 351 

98. Cippoletti weir 353 

99. Details of Cippoletti weir 354 

100. Scale to be screwed on side of Cippoletti weir 355 

101. Divisor attached to Cippoletti weir 356 

102. Turnout and measuring weir 357 

103. Device for diverting a constant quantity of water 357 

104. The need of storing water in reservoirs 359 

105. Rise of ground water from irrigation 374 

106. Chain puddler. Used in making canals watertight 376 

107. Modified chain puddler 377 

108. Wooden stave pipe carrying irrigation water 378 

109. Lateral lined with concrete 379 

1 10. Cement-lined main canal 380 

111. Pumping plant 382 

112. Drainage of irrigated lands by intercepting drains 383 

113. Structure of an alkali spot 386 

114. Quaternary Lakes of the Great Basin. Sources of alkali deposits. 389 

115. Effect of a strong solution of potassium nitrate on protoplasm. 392 

116. Vegetation on alkali lands 393 

117. Alkali rising in spots on irrigated pasture 396 



xxiv LIST OF ILLUSTRATIONS 

Fig. Page 

118. The annual rainfall of Milan compared with that of humid and 

arid districts in the United States 408 

119. Comparative yields of strawberries, irrigated and unirrigated 409 

120. An irrigation plant in Pennsylvania 412 

121. Distribution of water on Craigentinny Meadows, Edinburgh. . 416 

122. Section of cement flume 420 

123. Section of V-shaped flume 420 

124. Wooden flume , ... 420 

125. Section of rectangular flume 420 

126. Flume with lateral gate 421 

127. Buck scraper 421 

128. Leveler or float 422 

129. Shuart grader 422 

130. Soil auger 423 

131. Lateral plow 423 

132. V-crowder 424 

133. Building a ditch 424 

134. Typical forms of farm ditches 425 

135. Concrete drop in ditch 426 

136. Drop in flume 427 

137. Distributor for hose 428 

138. Attaching hose to distributor 428 

139. Leveling device 428 

140. Lateral headgate 429 

141. Concrete gate 429 

142. Dammer 429 

143. Board dam 429 

144. Canvas dam 430 

145. Canvas dam with opening 430 

146. Metal dam 430 

147. Distribution of water from flume to furrows 430 

148. Distribution through wooden tubes 430 

149. Lath check 431 

150. Conducting water down inclines in concrete pipes 431 

151. Roller furrower 432 

152. Utah lay-off and pulverizer 434 

153. Robinson's adjustable corrugator and renovator 434 

154. Ridger in check and basin irrigation 435 

155. Ridger in check and basin irrigation 435 

156. Furrower in action 435 

157. Cultivator 436 

158. Cultivator attachments 436 

159. Beet cultivator attachments 437 



LIST OF ILLUSTRATIONS xxv 

Fig. Pago 

160. Alfalfa renovator 438 

161. Clod crusher, pulverizer, leveler and smoother 438 

162. Frieze water register 439 

163. Device for measuring miner's inches 440 

164. Cross-section of canal for measurement of flow 440 

165. Current meters 44 1 

166. Grant-Mitchell meter 442 

167. Leveler in action 443 

168. Sagebrush land 446 

169. The Doon ....*. 447 

170. Shadof of Egypt or Paecottah of India 448 

171. Caravan crossing the plains in early irrigation days 455 

172. Irrigation canals are cut through the mountains 459 

173. Major J. W. Powell 463 

174. Completed diversion dam of the Truckee Carson, Nev., pro- 

ject of the United States Reclamation Service 465 

175. Steam power digs the modern canals 466 

176. View of the irrigation plant of the Utah Experiment Station. . . 467 

177. Dam of Salmon River project, Idaho, built by private enter- 

prise 468 

178. Plant for the study of the measurement and division of water. 469 

179. Work for a man 475 



ACKNOWLEDGMENT FOR 
ILLUSTRATIONS 

The illustrations in this book are either original or 
taken from the publications of the United States Depart- 
ment of Agriculture, the United States Geological Survey, 
and the state experiment stations, with the following 
exceptions, which have been secured from 

Bark, Don H., Irrigation Investigations, United States Department 

of Agriculture. Figs. 50, 58, 59, 71, 72, 76, 91, 108, 168, 177. 
Blinn, P. K., Colorado Experiment Station. Figs. 38, 86, 156. 
Blanchard, C. J., United States Reclamation Service. Figs. 6, 49, 

69, 87, 93, 110, 174. 
Bonebright, J. E., Montana Experiment Station. Figs. 18, 39, 60, 

61, 167. 
Cutler, Thomas R. Fig. 75 
Forbes, R. H. Figs. 22, 66, 83, 90, 117. 
Gillette, C. P., Colorado Experiment Station. Fig. 178. 
Greeley Commercial Club. Fig. 79. 

Harris, F. S., Utah Experiment Station. Figs. 16, 19, 26. 
Jardine, W. M., Kansas Agricultural College. Fig. 73. 
Jarvis, O. W., Superintendent, Southern Nevada Experiment 

Farm. Fig. 85. 
Johnson Company, The, Salt Lake City. Figs. 14, 17, 82, 92, 94, 

171, 172, 179. 
McLaughlin, W. W., Irrigation Investigations, United States 

Department of Agriculture. Figs. 52, 88, 151. 
Ogden Commercial Club. Fig. 81. 
Quinney, Jos. E. Jr., Fig. 75. 
Redland's Commercial Club. Fig. 34. 
San Jose Commercial Club. Fig. 13. 
Santa Clara Commercial Club. Fig. 89. 

Smith, George Otis, United States Geological Survey. Fig. 173. 
Winsor, Luther M., Utah Experiment Station. Figs. 68, 80, 175. 

Grateful acknowledgment is made of the assistance 
rendered by the above persons. 

(xxvi) 



THE PRINCIPLES OF IRRIGATION 
PRACTICE 



CHAPTER I 
THE MEANING OF IRRIGATION 

Water, soil, air and sunshine are the four great groups 
of physical forces that determine the growth of plants. For 
the production of plant crops, all of these must be present 
and active. Water, therefore, is essential to plant-growth 
and crop-production. 

The water that falls upon the earth in the form of rain 
and snow is the source of all the water used in agriculture. 
To be of value in plant-growth, this water must be stored, 
for longer or shorter periods, in the soil in which plants 
are growing. Whenever the soil becomes too dry or too 
wet, or if the total quantity is insufficient or too large, 
plant-growth is hindered. It is the concern of agriculture 
to maintain in the soil the proper quantity of water during 
the growth of crops. 

1. Annual rainfall. — Water, in the form of rain or 
snow, falls over the whole earth. No place is known where 
some rain does not fall at some time during the year. 
However, the quantity that falls varies greatly in different 
regions. Over the so-called deserts the annual rainfall is 
often less than 5 inches, while in various places near the 
seashore or among the mountains, the annual rainfall 

A (1) 



2 IRRIGATION PRACTICE 

exceeds 100 inches and occasionally reaches 600 inches or 
more, as at Assam, India. From district to district, the 
world over, the quantity of water that falls annually 
upon the farmers' fields is different. 

2. Seasonal rainfall. — Moreover, the time of the year 
at which the rain comes is not everywhere the same. In 
some localities the rain falls chiefly in summer, during 
the season of crop-growth; in others, during the spring; 
in others, during the fall, and in yet others, during the 
winter. Going eastward from the Pacific seaboard, this 
difference in seasonal rainfall is well brought out. In 
California, the heaviest rainfall comes during midwinter; 
in the Great Basin, in early spring; on the eastern slope of 
the Rocky Mountains, in late spring, and on the Great 
Plains, near midsummer. The annual rainfall may be 
fairly large in a given locality, but it does not necessarily 
fall at the time that plants are growing. 

3. Variations in rainfall. — Added to these variations 
in the quantity of total rainfall, and in the distribution 
throughout the year, is still another: The same quantity 
of rain does not fall in the same place from year to year. 
In one year there may be a large precipitation, and in 
another a very light one; and the time of the year of the 
heaviest downfall may be shifted somewhat from year 
to year. 

True, the variations are not large. The driest year 
seldom receives less than two-thirds the rainfall of the 
wettest year, and usually it receives more. True, also, so 
far as our records show, the average rainfall over a certain 
locality for ten or twenty years is practically constant. 
The average rainfall at any one place is nearly invariable, 
although distinct variations occur in successive years. 
(Fig. 1.) 



MEANING OF IRRIGATION 3 

4. Conservation of rainfall on farms. — It is the business 
of the farmer so to handle his farm that the largest possible 
proportion of the rain that falls may be made to enter the 
soil, and to remain there until needed by plants, unless, 
indeed, the rainfall is too heavy, when provision must be 
made for relieving the soil of the harmful surplus. To 
accomplish this, the farmer must resort to methods for 



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Fig 1. Progressive averages of annual rainfall (1834-1906). 

preventing, or reducing largely, the loss due to the run- 
off, evaporation and seepage. Where the annual rainfall 
is fairly large and well distributed, these methods are 
not applied extensively; but where the annual rainfall is 
light or is not in the growing season, moisture-conserv- 
ing methods are indispensable. There are relatively 
few localities on earth where special efforts to conserve 
the rains for plant-growth are not rewarded by large 
crop yields. The smaller the annual rainfall, the greater 
is, naturally, the return for careful moisture-conservation. 
5. Conditions of dry-farming. — If the annual rainfall 
be very light, it frequently happens that, with the best 
available tillage methods, the water conserved in the soil 



4 IRRIGATION PRACTICE 

is so small that only certain crops can be grown, and of 
these crops maximum yields are not obtained. The annual 
rainfall, below which special moisture-conserving methods 
are necessary, is different at different places. Ordinarily, 
where the rainfall is 20 inches or less, the special water- 
conserving methods of dry-farming must be used. Where 
the average temperature is high; where heavy winds 
blow largely; where the soils are shallow or infertile, or 
where other water-dissipating factors are especially 
active, the methods of dry-farming must be employed, 
even if the rainfall reaches 25 or 30 inches annually. On 
the other hand, with our present experience, we are 
obliged to admit that when the annual rainfall is less than 
10 inches, our present methods of water-conservation 
are not sufficient, except in a few special localities, to 
make profitable crop-production possible. 

6. Conditions of irrigation. — Wherever proper methods 
of manuring and tillage for water-conservation are insuffi- 
cient to produce uniformly profitable or maximum crops, 
irrigation is employed. The first aim of the farmer should 
always be to store as much as possible of the natural 
precipitation in the soil, and to apply water artificially 
only to make up the deficiency in the quantity of water 
required by plants. The quantity of irrigation water, 
then, needed on any farm, will depend on the care with 
which the rainfall is conserved for the use of plants. The 
more thoroughly water-conservation methods are prac- 
tised, the smaller the quantity of irrigation water required; 
the more carelessly the rain-water is conserved, the larger 
the quantity of irrigation water required. Irrigation 
should always be, and in a good system of agriculture 
always is, supplementary to the natural precipitation. 

7. Irrigation defined. — Irrigation is the artificial appli- 



MEANING OF IRRIGATION 5 

cation of water to lands for the purpose of producing large 
and steady crop yields whenever the rainfall is insufficient 
to meet the full water requirements of crops. Irrigation for 
the purpose of disposing of sewage is of limited extent, 
and is not always true irrigation. 

8. Geographical need of irrigation. — The field of 
irrigation, as above defined, is very large. About 25 per 
cent of the earth's surface receives 10 inches or less of 
rainfall annually, and, with our present knowledge, can be 
reclaimed only by irrigation. Another 30 per cent of the 




ffANGC 



Fig. 2. The limited water supply makes it unlikely that more than one-tenth of 
the land will be irrigated. The shaded area is irrigated. 

earth's surface receives between 10 and 20 inches of rain- 
fall annually. Over this vast area the chief extensive 
crops may be grown without irrigation, but the intensive 
crops demand the help of irrigation. That is, nearly 
six-tenths of the earth's surface will be reclaimed, if at 
all, by irrigation and dry-farming. The remaining four- 
tenths will be helped materially by a system of irrigation. 
9. Possible extent of irrigation. — The great rivers 
which, with their numberless tributaries, flow from the 



6 



IRRIGATION PRACTICE 



highlands through the arid and semi-arid lands, together 
with some of the underground waters, must be the source 
of the water to be used in irrigation. When a world-sys- 
tem of irrigation shall be perfected, all of the available 
water will not, in all probability, cover more than one- 
tenth to one-fifth of the thirsting land. The remainder 
must be left to be conquered by dry-farming methods. 
Yet, the possible area to be reclaimed by irrigation is 




Fig. 3. The value of water in an arid land. A Papago 
squaw, in Arizona, utilizing the drip from her water 
bottle to grow a lew onion plants beneath, protected 
by a paling of sticks. 

tremendous; and in view of its certainty of large crop 
yield, farming under irrigation should be the most attrac- 
tive of all modes of farming. (Fig. 2.) 

Irrigation will further find a limited application in 
humid countries, the occasional dry years of which cause 
injurious droughts. In many of the humid regions the 



MEANING OF IRRIGATION 7 

methods of dry-farming will often be found to be as 
effective and less expensive. 

10. Mission of irrigation and dry-farming. — Irriga- 
tion and dry-farming go hand in hand in reclaiming the 
great countries under a low rainfall, and in forever banish- 
ing drought from the earth. In this volume the principles 
underlying a rational practice of irrigation are discussed. 
The dry-farming methods involved in irrigation are only 
touched upon in passing, for they have already been some- 
what fully discussed in another volume.* 

REFERENCES 

Henry. Weather Bureau, United States Department of Agricul- 
ture, Bulletin No. D. 

Mead, Elwood. Irrigation Institutions. The Macmillan Company. 

Newell, F. H. Irrigation. T. Y. Crowell & Co. 

Smythe. Wm. E. The Conquest of Arid America. The Macmillan 
Company. 

Widtsoe, J. A. Dry-Farming. The Macmillan Company (1910). 

♦Widtsoe, J. A., Dry-Farming: A System of Agriculture for Countries under a 
Low Rainfall. The Macmillan Company, New York. 



CHAPTER II 
SOIL MOISTURE 

All bodies in the universe attract each other. The 
greatest sun in the heavens and the smallest speck of dust 
under the microscope are mutually attracted. This 
universal force of attraction finds different expressions 
under varying conditions. Thus, the heavenly bodies, 
immense distances apart, are given definite motions and 
are held in their places by their mutual attractions. 
Bodies near the earth and belonging to it, instead of revolv- 
ing in space, fall to the ground by virtue of this attrac- 
tion which the earth exercises upon all bodies on or near 
its surface. In both these cases the attracting bodies are 
considerable distances apart. 

11. Attraction between near bodies. — When the 
attracting bodies are brought very near each other, within 
reach of the molecular forces, which, probably are only 
expressions of the universal force, special attractions 
are observed. For example, if two plates of glass, evenly 
and highly polished, are laid upon each other they adhere 
so firmly that it is practically impossible to separate 
them. A square of iron, with a highly polished surface, 
may be lifted by simply lifting a similar square which 
has been placed on the lower square with the polished 
surfaces in contact. Two pieces of lead, with clean sur- 
faces, will adhere very firmly, as will also india-rubber, 
wax and similar substances. These attractions act only 
through extremely small distances. If the polished plates 

(8) 



SOIL MOISTURE 9 

of glass are separated by the thinnest piece of paper, 
they do not adhere; if the iron surfaces are a trifle dusty 
they do not adhere. The distance apart determines 
the adhesion. 

It is generally held that the ultimate particles of all 
substances are held together by molecular attractions. 
Iron is a solid mass and not a pile of loose particles, 
because of the mutual attraction of like particles, known as 
cohesion. These molecular forces may be overcome by 
other forces, notably by heat. When the solid iron is 
heated, the molecular attraction is weakened until the 
iron is melted. If the heating is further continued, the 
molecular attraction is finally overcome, and the iron 
becomes a gas, in which state the ultimate particles, or 
molecules, actually repel each other. 

This theory of attraction is of great help in under- 
standing the phenomena observed in soils, especially in 
relation to water. When a pebble is dipped in water, a 
thin water-film clings around its whole extent. The water 
has come into very close contact with the surface of the 
pebble, within the reach of molecular forces, and a cer- 
tain quantity of water adheres. The quantity of water, 
thus adhering, is just in proportion to the force of adhesion 
existing between the water and the rock surface. On the 
basis of this fact — the adhesion between rock surfaces 
and water — rest the tillage methods of moisture-conser- 
vation. 

12. Soil particles. — Soil is composed of broken-down 
rock mixed with decaying animal and plant remains. The 
most notable properties of soil result from the minute 
size of the constituent particles. The coarsest particles 
useful to plants are from 1 to 3 millimeters in diameter, 
which means that about twenty-three placed side by side 



10 



IRRIGATION PRACTICE 



would make an inch. The finest are about .00001 milli- 
meter in diameter; and it would require about 25,000 of 
them, placed side by side, to make an inch. Most of the 
particles in an ordinary soil are of a size intermediate 
between these extremes. 

The smallness of the soil particles means that the 
number of them, in an acre of ground to a depth of one 
foot, fairly transcends the human mind. If a soil were 
made up entirely of the coarsest particles above men- 
tioned, there would be, in 1 cubic inch, 12,167; if of the 
finest, there would be in 1 cubic inch, 15,625,000,000,000 
particles. These vast numbers of soil grains of all sizes 
between the extremes given, are jumbled together in the 

soil in every conceiv- 
able manner. Groups 
and clusters of them 
are formed; the larger 
ones touch in few 
points, while the 
smaller ones fall into 
the spaces between, 
and lime and other 
substances often cause the cementing together of parti- 
cles. The relatively large air spaces between the particles 
and groups form from 30 to 60 per cent of the whole 
soil volume. These open or air spaces are sometimes 
spoken of as pores or tubes. They are of infinite com- 
plexity of shape and direction as they wriggle through 
the soil mass. In spite of the immensity of the numbers 
and variety of the sizes of the particles, the whole 
porous sytem is held together as one, and possesses 
definite properties. 

Of chief agricultural interest is the surface exposed 




Fig. 4. Soil is a mixture of particles of very- 
varying size. 



SOIL MOISTURE 11 

by the soil particles, for it is to these surfaces that the 
soil water clings, and from them that the plant-food is 
largely derived. It is naturally very difficult to make 
this determination accurately, but approximate figures 
may be given. One pound of the coarsest particles above 
mentioned would expose an area of about 11 square feet; 
while one pound of the finest particles would expose 
about 110,538 square feet or more than 2}^ acres. The 
surface of the soil particles in 1 cubic foot of an average 
soil, lying between the two extremes described above, 
would be nearly 50,000 square feet. The finer the soil, 
the larger would be the surface of the soil particles. 
This immense surface exposed by the particles of agri- 
cultural soils is of the highest importance in agriculture. 

13. The soil-moisture film. — The result of the attrac- 
tion between water and rocks is that water added to a 
soil forms a film over the surfaces of the particles. This 
film is continuous so far as the water goes, covering every 
particle, bridging every point of contact and filling every 
minute opening, the diameter of which is not greater 
than the distance through which the forces of adhesion 
act. True, in every soil, even in those composed of the 
smallest particles, when the soil-water film is of maximum 
thickness, the majority of the soil pores, which are much 
larger than the distance through which adhesion attrac- 
tion can act, are open and free from water except as a 
thin film may cling to their sides. The shape of this film, 
as it fits accurately over every exposed surface, is a sym- 
bol of multiplied complexity that completely baffles 
human description or understanding. 

When a given quantity of water is added to a given 
weight of soil, the thickness of the resulting soil-mois- 
ture film depends entirely on the fineness of the particles 



12 IRRIGATION PRACTICE 

constituting the soil. This must of necessity be so, for, 
as has been shown, the smaller the soil particles the 
larger is the surface exposed; and the larger the surface, 
the thinner will be the film produced by a given quantity 
of water. The thickness of the soil-moisture film is of 
considerable importance, for from it plants secure the 
water needed in their growth. If the film be too thin, 
that is, if it is held very firmly, plants are not able to move 
it from the surface of the soil particle. 

14. Thickness of film and diameter of particle. — A 
definite mathematical relationship exists for any per 
cent of moisture between the thickness of the soil-mois- 
ture film and the diameter of the soil grains. If a soil of a 
specific gravity of 2.75 contains 5 per cent of water, the 
thickness of the soil-moisture film is slightly more than 
two hundredths of the average diameter of the soil grains; 
if 10 per cent, a little more than four hundredths; if 20 
per cent, not quite eight hundredths; if 30 per cent, a 
little more than eleven hundredths; and if the soil con- 
tains 40 per cent of water, the thickness of the soil-mois- 
ture film is about fourteen hundredths of the average 
diameter of the soil grains. 

That is, the thickness of the soil-moisture film in soils 
that contain from 5 to 40 per cent of moisture, varies 
from two hundredths to fourteen hundredths of the 
diameter of the average soil grains. When the very small 
sizes of the particles themselves are considered, this 
shows the extreme thinness of the soil-moisture films, 
with which agriculture has to deal.. Meanwhile, it must 
be remembered that only very fine soils can hold as much 
as 40 per cent of water. When the thickness of the soil- 
moisture film is somewhere in the neighborhood of one 
fifty-thousandth of an inch, it is probably near its maxi- 



SOIL MOISTURE 13 

mum thickness, and, when this has been reached, there are 
in average soils about 20 per cent of moisture. 

15. Hygroscopic coefficient. — If a thoroughly dried 
soil be exposed to air, which is always somewhat moist, 
the attraction between the soil surface and the water 
vapor in the air immediately becomes active. Some of 
the water vapor condenses upon the surfaces of the soil 
grains to form the beginnings of the film. This coating 
of water is hygroscopic soil moisture. If the air sur- 
rounding the soil is saturated with water vapor, the 
largest possible quantity is condensed upon the soil. 
The percentage of moisture representing the full con- 
densation of water upon soil from such saturated air, 
under given conditions of temperature, is known as the 
hygroscopic coefficient. 

The water thus taken from the air is not wholly held 
as surface film. In every soil are certain substances 
(colloidal) that absorb water to form loose chemical com- 
binations. Such materials are well represented by the 
jellies which hold large quantities of water uniformly 
distributed throughout their mass. Among the substances 
with more or less strongly marked jelly-like properties 
are clay, hydrate of iron, humus and decaying organic 
matter generally, and a number of gums, among which 
gum tragacanth is the most notable. 

The hygroscopic coefficient, therefore, increases as 
the fineness of the soil increases, and as the quantity of 
the water-absorbing substances increases. For example, 
Lyon and Fippin found that very fine sand absorbed 1.8 
per cent of hygroscopic moisture; silt, 7.3 per cent; clay, 
16.5 per cent, and a muck soil absorbed 48 per cent of 
water from saturated air. Hilgard examined three soils 
very much alike, except that one contained 4 per cent, 



14 IRRIGATION PRACTICE 

the other 19.83 per cent, and the third 51 per cent of iron 
hydrate. The hygroscopic coefficient of the first was 
4.92 per cent; of the second, 15.40 per cent, and of the 
third, 19.66 per cent. At the Utah Station it was found 
that on the dry-farms, in the fall, after the baking heat 
of summer and before the autumn rains, the soil moisture 
remaining was in proportion to the clay contained by 
the soils. 

The hygroscopic moisture is held very firmly by the 
soil, and it is very doubtful if it has any direct value for 
plants. The part clinging around the soil grains probably 
has no such value, but it is possible that the colloidal 
soil constituents often containing much water may be 
made to give up some of their water to the growing plant. 
King has suggested that in seasons of drought the hygro- 
scopic water may evaporate at one point in the soil and be 
condensed elsewhere upon the root-hairs in search of water. 
The chief agricultural interest of hygroscopic soil mois- 
ture is that upon it and possibly in part by it, is held the 
water which really can be used by plants. 

16. The wilting coefficent. — Water added to a soil, 
the hygroscopic coefficient of which has been satisfied, 
simply thickens the soil-moisture film or more com- 
pletely saturates the colloidal soil constituents. The 
first water thus added above hygroscopic saturation is 
also held very firmly and is of little or no direct value to 
plants. As more water is added, however, and the film 
is thickened around the soil grains, the outer layers of the 
film water are held with less and less force, and a point 
is at last reached above which plants can use the soil 
moisture in growth, although it may be with some diffi- 
culty. Whenever the soil moisture in a cropped field is 
reduced to this point, the plants growing on the soil 



SOIL MOISTURE 15 

begin to wilt, and growth practically ceases. The per- 
centage of moisture corresponding to this point is called 
the wilting coefficient. 

According to the researches of Briggs and Shantz, 
the wilting coefficient is about one and one-half times the 
hygroscopic coefficient. That is, in a soil with a hygro- 
scopic coefficient of 6 per cent of water, the wilting coeffi- 
cient would be about 9 per cent. This relative value of 
the wilting coefficient appears to be confirmed by field 
experiments conducted at the California and Utah 
Experiment Stations. 

The wilting coefficient, like the hygroscopic coefficient, 
varies with the soil used. In sandy soils it is low, often 
less than 1 per cent of moisture; in clay soils higher, 
often more than 16 per cent, and in extremely heavy clays 
as high as 30 per cent; in the average loam, about 10 per 
cent of moisture. It is ordinarily thought that plants 
differ markedly in their power of reducing the soil mois- 
ture before wilting. Recent researches do not bear out 
this view. On a given soil, under like meteorogical con- 
ditions, the wilting coefficient is within 1 to 3 per cent 
of each other for all the ordinary plants at the same 
period of growth, whether grown under arid or humid 
conditions. 

While growth undoubtedly ceases at wilting, yet the 
plant may slowly take up some of the moisture held 
in the soil below the wilting point. On the other hand, 
under proper methods of agriculture the soil moisture is 
seldom reduced to the wilting point, especially on deep 
soils, if irrigation has been practised regularly. At the 
Utah Station, several crops, in their medium stages of 
growth, were allowed to go for long periods, from twenty- 
seven to fifty-five days, without irrigation. At the close 



16 



IRRIGATION PRACTICE 



of the periods, the grain crops and the peas were prac- 
tically ripened. No noticeable injury from wilting was 
observed. Some of the results are presented in the fol- 
lowing table: 



Crop 



Wheat . 
Oats . . 
Corn 
Peas . . 
Lucern 
Potatoes 



Days 

after 
irrigation 



Per cent 

of water in 

first foot 



38 
32 
47 
27 
31 
31 



8.26 
7.57 
9.28 
7.66 

9.07 



Average per 

cent of water 

to a depth of 

6 to 8 feet 



8.21 

9.98 

10.03 

10.68 

8.34 

11.62 



The hygroscopic coefficient of the soil was about 5 
per cent, which would make the wilting coefficient about 
73^2 P er cent. In only one case, that of wheat, did the 
soil moisture go below this point in the first foot; and, in 
every case, the percentage of soil moisture to a depth of 
6 to 8 feet, through all of which root-action was felt, was 
above the calculated wilting coefficient. 

17. Lento-capillary point. — The water in the soil- 
moisture film corresponding to the wilting coefficient is 
held so firmly that plants can absorb it with difficulty. 
As more water is added to the soil, to thicken the film, 
the more loosely is the water held, and consequently the 
more easily can plants secure it. As this thickening 
goes on, a point is reached above which the film water is 
held so loosely that it moves freely from soil particle to 
soil particle under the influence of the forces in the soil. 
This has been called the lento-capillary point. The water 
above this point is readily available to plants, and con- 
stitutes the main supply of water for plants under irri- 
gated conditions. 



SOIL MOISTURE 17 

Whenever the soil moisture is above the lento-capil- 
lary point, plants secure their water with the least expendi- 
ture of energy, and it should therefore be the purpose 
of irrigation to maintain the moisture in the soil above 
this point, at least during the periods of most rapid plant- 
growth. In practice, this is usually done, except in sea- 
sons of water-shortage. The practical irrigator recog- 
nizes the need of irrigation by a faint change in the color 
and rigidity of the plants — possibly a condition prelim- 
inary to wilting. When this occurs, the soil moisture is 
ordinarily just above or below the lento-capillary point. 

During two summers, on the experimental fields of 
the Utah Experiment Station, the moisture in the soil 
was determined immediately before each of several hun- 
dred irrigations. In the first year, the percentage of soil 
moisture was 13.17; in the second, 13. In every case, 
the practical irrigator declared the field in need of irriga- 
tion. The lento-capillary point was determined for this 
soil to be about 12.68 per cent, or almost identical with 
the percentage of soil moisture at which irrigation was 
declared advisable. 

18. Maximum capillary capacity. — As the soil-mois- 
ture film is thickened by the further additions of water 
above the lento-capillary point, the force with which the 
outer layers of water is held becomes weaker and weaker. 
At last a point is reached above which no more water 
can be taken up. When this thickness of the film is 
reached, new additions of water simply slide off the film 
and are drawn away by gravity. This is the point of 
maximum capillary capacity. 

19. Free water. — Water added to a soil above the 
maximum capillary capacity is called free water. It 
moves slowly downward through the pores and tubes of 

B 



18 IRRIGATION PRACTICE 

the soil until it is all absorbed by the lower drier soil or 
until it communicates with the standing water-table. 

Soil moisture is the term used to designate the water 
held in the capillary condition in soils. Soil water denotes 




Fig. 5. The moisture film surrounding a soil particle. The black part represents 
a segment of the particle. (6) Hygroscopic coefficient; (c) wilting coeffi- 
cient; (d) lento-capillary point; (e) point of maximum capillarity; (d-e) 
freely moving capillary moisture. 

the free water, that beyond capillary saturation, which 
may exist in soils. Many books on agriculture speak of 
the maximum water capacity of soils, meaning the water 
held in a volume of soil artificially confined in a funnel or 



SOIL MOISTURE 19 

tube, when the air spaces in the soil are completely filled 
with water. This constant has no great agricultural value. 
It represents a condition that should be avoided so far 
as is possible in farming under irrigation, except in the 
top foot of the soil while water is actually being applied 
to the land. 

20. Summary. — The principles upon which rational 
irrigation practices are built, rest upon the facts pre- 
sented in this chapter. The attraction existing between 
soils and water causes water to cling as a film around the 
soil grains. The hygroscopic coefficient represents the 
water which is condensed from the water vapor of sat- 
urated air; it is of no practical value to plants. The wilt- 
ing coefficient, about one and one-half times the hygro- 
scopic coefficient, represents the point below which plants 
can not secure sufficient water from the soil for their needs. 
The lento-capillary point is the point above which the 
soil moisture is readily available to plants. Above this 
point, also, film water moves freely in obedience to the 
laws of capillarity. The maximum capillary capacity 
represents the point at which the attraction between 
the soil surface and water ceases to be active; it is satu- 
rated. From the first hygroscopic coating to the maximum 
capillary water capacity, the water is said to be in a capil- 
lary state. Any water added above this point is free 
water moving in obedience to the pull of gravity. (Fig. 5.) 

Much excellent work has been done on soil moisture 
by investigators, both in Europe and America. F. H. 
King, E. W. Hilgard, Milton Whitney and his associates, 
have done much of the American work. Unfortunately, 
for the arid regions, most of the work on soil moisture 
has been done under humid conditions. For instance, 
capillarity has been studied almost entirely by placing 



20 IRRIGATION PRACTICE 

tubes filled with soil in pans containing water, and the 
upward movement has been studied. This is of little 
interest to the arid regions. Much profitable work may 
be done for irrigation by the careful study of the move- 
ment of water applied to soils as under irrigated 
conditions. 

REFERENCES 

Briggs, Lyman J. The Mechanics of Soil Moisture. United States 

Department of Agriculture, Bulletin No. 10 (1897). 
Briggs, Lyman J., and Shantz, H. L. The Wilting Coefficient for 

Different Plants, and Its Indirect Determination. United 

States Department of Agriculture, Bureau of Plant Industry, 

Bulletin No. 230 (1912). 
Hilgard, E. W. Soils. Chapters VI and XIII (1906). 
King, F. H. Physics of Agriculture. Chapters IV and V (1901). 
Widtsoe, J. A., and McLaughlin, W. W. The Movement of 

Water in Irrigated Soils. Utah Experiment Station, Bulletin 

No. 115 (1912). 



CHAPTER III 
THE SOIL AS WATER RESERVOIR 

In an ideal system of irrigation, water would be 
applied continuously to the soil, and at a rate to meet 
the actual requirements of the plants growing on it. 
Except in a very few cases, this ideal method is impossi- 
ble. In practice, lands are watered intermittently. 
When the "turn to water" comes, the farmer applies to 
the soil in a few hours, or in a few days at most, as much 
water as he is allowed, or as he believes will supply the 
crop until the next turn comes, which may be a few days 
or several weeks hence. Even in cases where the farmer 
has at his disposal a continuous flow of water, it is sel- 
dom practicable or wise to attempt continuous irrigation 
of any one field. Irrigation is essentially an intermit- 
tent practice. 

Plants can not live long without water. When the 
water in the soil is reduced to the definite limit known as 
the wilting coefficient, plants may be seriously injured in 
a few hours, unless more water is added to the soil. In 
view of this fact and the common knowledge that crops 
thrive under systems of irrigation-rotation, it is evi- 
dent that water applied in irrigation is held by the soil 
in quantities sufficient to maintain crops in a good con- 
dition until the next watering occurs. That is, water 
may be stored in the soil in considerable quantities. The 
property of soils to act as storage reservoirs for water is 
of the highest importance in the practice of irrigation. 

(21) 



22 IRRIGATION PRACTICE 

21. Irrigated soils are unsaturated. — In all proper 
irrigation practice, the farmer is dealing with unsaturated 
soils. Many of the best results of irrigation are due to 
this condition; and the irrigation practices to be out- 
lined refer largely to soils which are not fully saturated 
with water. 

Water should ordinarily be applied to crops when the 
water in the soil has reached the point of lento-capillarity 
as described in the preceding chapter; that is, the point 
below which capillary movements become very slow. 
When the soil water has been exhausted to this point, 
the plant is obliged to expend an unnecessary amount of 
energy in securing water, and the soil should be irrigated. 
Experienced, practical irrigators declare that irrigation 
is necessary about the time this point has been reached. 
It may usually be recognized by a flabbiness and a slight 
change of color in the leaves and stalks of the plants. 

The percentage of moisture in the soil which corres- 
ponds to this point of slow capillary motion varies accord- 
ing to the fineness of the soil. In coarse soils it may be 
below 10 per cent; in fine clayey soils, 20 per cent or 
more. For average loam soils it is in the neighborhood 
of 12 or 13 per cent. 

The maximum capacity for capillary soil moisture 
also varies with the soil. In coarse sandy soils it fre- 
quently falls to 12, or even 10, per cent; in fine clayey 
soils it rises to 30 or 40, or more, per cent. In average 
loam soils it is not far from 24 per cent. 

The water actually used in a wise system of irrigation 
varies, then, between the maximum capillary saturation 
and the point of lento-capillarity, which, in an ordinary 
loam soil, is a variation of from 24 to 12 per cent. This 
must be supplied from time to time by irrigation; but, 



SOIL AS WATER RESERVOIR 23 

the usual quantities of water added in irrigation seldom, 
if ever, are sufficient to bring the soil beyond the first or 
second foot to maximum capillary saturation. 

The quantity of water that may be applied in any one 
irrigation depends somewhat upon the nature of the soil, 
yet varies within rather narrow limits. It is seldom pos- 
sible to apply at one irrigation less than 2 inches, and 
practically impossible to apply more than 10 inches, 
unless the soil be very gravelly. The practical limits are 
yet narrower; a light irrigation is about 3 inches, a heavy 
one about 8 inches; and an average one from 5 to 6 inches. 

One inch of water is equivalent to 3 per cent of soil 
moisture to a depth of one foot. A heavy irrigation of 
8 inches would, therefore, raise the soil moisture in 1 
foot of thoroughly dry loam soil to 24 per cent, or maxi- 
mum capillary saturation. If the soil, at the time of 
irrigation, contains 12 per cent of moisture, one such 
heavy irrigation would raise 2 feet of soil to full capillary 
saturation. Since the moisture in the upper 8 to 10 feet 
is concerned in plant-production, the full, soil column 
under such irrigation is far from saturation. In fact, a 
loam soil, containing 12 per cent of moisture, will con- 
tain, after receiving a heavy irrigation of 8 inches, not 
more than an average of 15 per cent to a depth of 8 feet; 
while the full saturation is about 24 per cent. With a 
medium irrigation of about 5 inches the unsaturated 
character of the soil would be still more marked. 

22. The movement of soil moisture. — The water 
added to soils by irrigation, instead of saturating the 
upper soil a foot or two, distributes itself with great 
regularity to considerable depths in the soil. All soil 
moisture is acted upon by the two chief contending 
forces of gravitation and adhesion. Gravity tends to 



SOIL AS WATER RESERVOIR 25 

pull the moisture downward, while the attraction between 
the soil and the water tends to hold it as a film around the 
soil grains. The actual movement of a particle of water 
in a soil is a resultant of these forces. 

In general, water moves from the thicker to the 
thinner soil film. Immediately after an irrigation, when 
the upper soil layers are wettest, the water moves down- 
ward; immediately before an irrigation, when the plants 
have largely exhausted the upper soil layers of water, 
the soil water is moving slowly upward. The down- 
ward movement, aided by gravity, is more rapid than 
the upward movement against gravity. The film of soil 
moisture is usually in a state of motion, attempting to 
place itself in equilibrium with the many contending 
forces in the soil. As examples, the moisture in the soil 
moves in all directions toward a point at which a root- 
hair is absorbing water; and, as evaporation occurs at 
the soil surface, there is a general upward movement of 
the soil moisture to supply the loss. 

The drier the soil, the slower does the soil moisture 
move. Under the point of lento-capillarity, soil-mois- 
ture movements occur with great difficulty; above this 
point, they occur with great freedom. One proof of this 
is that at depths of 8 to 10 feet, where plant roots pene- 
trate in small numbers only, the moisture is seldom 
reduced below the lento-capillary point, while nearer 
the surface and abundant root-action the moisture is 
often reduced to the wilting coefficient. 

23. The distribution of soil moisture. — After a sur- 
face irrigation of a soil with a water content near the 
lento-capillary point, the upper soil layers are invariably 
wetter than the lower ones. Any deviation from this rule 
is only apparent and is due to the fact that the subsoil 



26 



IRRIGATION PRACTICE 



contains more clay or other fine particles than the top 
soil, and therefore has a higher water-holding power per 
unit weight of soil. When the thickness of the soil-mois- 
ture film is considered, there is, immediately after an 
irrigation, a steady diminution with increasing depth. 
In soils of approximately uniform structure, this is well 
brought out, as in the following table, taken from the 
work of the Utah Station. In this table are shown the 
percentages of water in each foot to a depth of 8 feet, 
one or two days after irrigations of various depths, and 
in early spring after the winter precipitation has dis- 
tributed itself. 





Depth of water applied 


In the 
spring 




7.5 
inches 


5 inches 


2.5 
inches 


2d foot 


23.80 
21.88 
20.17 
17.72 
15.91 
14.55 
14.21 
14.15 


23.56 
20.73 
19.09 
17.84 
16.29 
15.83 
15.60 
14.81 


18.57 
13.81 
13.53 
13.46 
12.32 
11.81 
12.31 
12.70 


18.42 
17.49 


3d foot 


15.65 


4th foot 


14.07 


6th foot 


13.98 
13.14 


7th foot 


13.26 


8th foot 


12.93 







This distribution of soil moisture may be explained 
as follows: Water added to a soil first saturates the upper 
soil layers thoroughly, and there is a tendency to keep 
the top soil as near as possible to this point of maximum 
capillary saturation. Then, the lower drier layers begin 
to draw water downward. The wettest particles are near 
the top; the lower particles are all attracting the water. 
As water moves downward through the thin capillary 
film, friction has to be overcome. The farther the parti- 
cle is away the more friction must be overcome. The 
water above the point of lento-capillarity therefore 



SOIL AS WATER RESERVOIR 



27 



tends to distribute itself inversely with the distance of a 
soil particle from the wettest particle which is the source 
of supply; that is, after an irrigation, the soil-moisture 
film will be thickest in the top foot, and will become 
steadily thinner in the lower soil layers. (Fig. 7.) 

If the soil is very dry, say near the wilting coefficient, 
when an irrigation occurs, the downward movement 
of water is slow. Under such a condition the upper soil 
sections remain saturated until the moisture in the lower 



Percent of 14/ofer /n tso// 
o s /o /j 9.0 



as 




S 



10 



Fig. 7. Distribution of water in soil immediately after an irrigation. 



28 IRRIGATION PRACTICE 

layers has gone above the point of slow capillarity. 
Whenever that has been done, the moisture moves down- 
ward freely in obedience to the law already stated. This 
is really a matter of common experience, in opening any 
irrigation project in the arid region. The farmer finds 
that the water does not penetrate the soil deeply the 
first year of irrigation; but, as time goes on, the soil 
becomes wetter to greater depths, and at the same time 
less water is required to produce crops. The moisture 
content of the native undisturbed soil in arid regions is 
usually below the point of lento-capillarity. The first 
water added is used to bring the moisture content up to 
this point. As this is accomplished, water moves downward 
freely; and plants, also, are enabled to secure their water 
supply with a smaller expenditure of energy. 

The above law of distribution, which appears to hold 
for all unsaturated soils, above lento-capillarity, is a 
provision of nature of utmost importance in the economic 
use of irrigation water. Though water moves steadily 
downward after an irrigation, by far the largest propor- 
tion is held near the surface where plants can use it. It 
has been roughly estimated, on the basis of the law of 
distribution, that on a deep soil with a moisture per- 
centage at the point of lento-capillarity, 85 per cent of 
a heavy irrigation will be held in the upper 10 feet, within 
reach of plants. By reducing the irrigations properly, it 
is possible to prevent practically any of the irrigation 
water from descending below the zone of plant activity. 
On the other hand, if water is applied to a soil too fre- 
quently or in excessive quantities, the excess will slide 
downward to great depths, to reappear somewhere as 
seepage or drainage water. A good understanding of this 
principle, properly applied in irrigated districts, will do 



SOIL AS WATER RESERVOIR 29 

much to lessen the danger of injury from water-logged 
and alkali lands. 

In ordinary practice, lands should not be irrigated 
until the crop has reduced the soil-moisture content 
nearly to the lento-capillary point, and a little lower in 
the upper layers. Then only enough water should be 
applied to supply the zone of crop-action, say 10 or 12 
feet. This quantity varies, in different soils, but seldom 
exceeds a depth of 6 inches at an irrigation. 

24. Field moisture capacity. — The law of distribu- 
tion of water in soils makes it clear that the average 
percentage of water held in a soil to a depth of say 10 feet, 
after even a heavy irrigation, is far below the maximum 
capillary water capacity. Under the conditions prevail- 
ing in irrigated districts, except when over-irrigation is 
practised, the top foot or often the top layer contains 
only the maximum capillary percentage of moisture. 
The percentage becomes steadily smaller with increasing 
depth until, at 8 to 15 feet, it is very little above the 
point of slow capillary motion. This is especially well 
brought out in the spring, in districts where the precipita- 
tion comes chiefly in the winter time. In early spring, 
after the water from the winter snows and rains has 
soaked into the soil and distributed itself, it was 
found that, in the Utah experiments, a soil with a maxi- 
mum capillary capacity of 25 per cent invariably con- 
tained, to a depth of 8 feet, an average of 18 or 19 per 
cent of moisture. Crawley observed similarly that certain 
Hawaiian soils of a maximum capillary capacity of 32 to 
39 per cent contained in the field only 22 to 29 per cent 
of moisture. The percentage of moisture held in field 
soils to a depth of 8 to 10 feet, when the top foot is 
saturated, may be called the field water capacity of a 



30 IRRIGATION PRACTICE 

soil. It is not far from the optimum water content for 
plant-growth. 

25. Water distribution in furrow irrigation. — Wher- 
ever the water supply is plentiful, irrigation by some 
form of the flooding method is largely employed. Where 
water is scarce and smaller quantities must cover equal 
areas of land, the furrow method of irrigation is almost 
invariably practised. With certain crops, and on certain 
lands, even if the water supply is large, the furrow 
method of irrigation is preferred. 

Water applied in a furrow moves not only vertically 
downward, but in every direction from the wetted fur- 
row. The movement downward, aided by the full force 
of gravity, is the most rapid; it diminishes as it becomes 
more horizontal. That is, the lateral is smaller than the 
downward movement. It is a common experience that 
the lateral capillary movement of water near the surface 
of deep soils, is slight. In an average loam soil it is sel- 
dom more than 6 feet from the wetted center; in clay 
soils iarger; in sand soils smaller. The law of distribution 
is of the same nature as for the downward movement. 

If neighboring furrows are not too far apart, the 
moisture films moving in all directions from them finally 
meet, until, at certain depths, depending on the nature 
of the soil the size and distance apart of the furrows, and 
the quantity of water used, the percentage of water is 
practically the same, whether under or between the fur- 
rows. Loughridge, in a study of California orchards, 
when the furrows were from 6 to 8 feet apart, showed this 
to be true for a variety of soils. In the Utah work, on a 
loam soil, at depths of 5 and 6 feet, there was little dif- 
ference in the moisture content under furrow or row, 
when the furrows were about 3 feet apart. The longer 



Clay Loam. Sandy Soil. 

lit fit Ml. £Jt. Zit. 1ft. lit. Zit 



1 1 I I 1 1 1 1 I f T""T TTT "Ht I flf Fril l 1 1 1 i 1 1 1 TTT 



in. 

Zit. 
3 it 

SURFACE 
IJt 

Zit 

35t 

4U. 
5H. 




72 HOURS AFTER IRRIGATION 
Fig. 8. Distribution of water in soil under furrow irrigation. 



(31) 



32 IRRIGATION PRACTICE 

the water flows, the more completely will the lower soil 
layers be provided with the same percentage of water. 
In all cases, the law of distribution will be the same, 
except as modified by the full or partial help given by 
gravity, according to the direction in which the move- 
ment is taking place. (Fig. 8.) 

26. Effect of hardpan. — A layer through which water 
can pass with great difficulty, if at all, is often found a 
short distance below the soil surface. Sometimes it is 
merely the "plowsole," resulting from the repeated plow- 
ings of a somewhat clayey soil to the same depth. More 
often it results from the mutual relations of climate and 
soil. For example, in a country where the rainfall is 
heavy, the very fine particles of a heavy clay soil are 
washed downward, until the whole subsoil becomes more 
or less impervious to water. In regions of light rainfall, 
that is, in true dry-farming and irrigation regions, this 
washing down of fine material stops abruptly at a point 
representing the depth of penetration of the rainfall. 
Approximately the same quantity of rain falls from year 
to year on a certain soil. In the course of time there is 
formed at this point an accumulation of material com- 
monly called hardpan. Under a light rainfall, on a clay 
soil, the hardpan may be only a foot or two below the 
surface; on a sandier soil, from 4 to 10 feet, or even more, 
below the surface. Students of arid soils often estimate 
the annual precipitation of rain and snow by the depth 
of the hardpan. 

Not only are the fine clay and silt particles washed 
downward by the rains. Lime and other similar sub- 
stances are dissolved by the descending water, which 
cement together firmly the materials of the hardpan. 
Such calcareous hardpans are often so hard that they 



SOIL AS WATER RESERVOIR 33 

can be broken only by explosives, and, usually, in the 
beginning are impervious to water. 

As the practice of irrigation continues, the hardpan 
formed by the natural precipitation is softened, the 
materials of which it is made are distributed over larger 
soil depths, and frequently it wholly disappears. 

Under vast areas of the soils of arid regions, and not 
far from the surface, are found layers of shale or other 
stone. These were deposited by geological forces upon 
the soils then existing, and later, through ages, new soils 
were deposited upon these layers. In other cases, the 
original rock is only a few feet below the surface. Such 
hindrances to the free descent of water cannot, of course, 
be removed by frequent irrigation. 

An impervious layer a short distance below the sur- 
face, whether of a temporary or permanent nature, 
establishes conditions which change the laws of distribu- 
tion of water in soils as outlined previously in this chap- 
ter. When the irrigation water, in its descent, encounters 
the hardpan, the downward movement stops, the soil- 
moisture film thickens; if more water is added, water 
accumulates on the hardpan and fills the soil pores, thus 
producing an undesirable habitat for the plant-roots, 
and leads to serious crop injury. 

A soil underlaid with hardpan is always in danger of 
being water-logged, for the tendency is to apply as much 
water to such soils as to deeper lands. True, as will be 
shown later, in wet soils plants use more water than in 
dry ones. Yet, ordinarily, more water is added than 
plants can use. Moreover, the excess of water in the soil 
is a positive hindrance to successful plant-growth. Soils 
underlaid with hardpan should be irrigated more mod- 
erately and more frequently than deeper soils. It is often 
c 



34 IRRIGATION PRACTICE 

found profitable to blast occasional holes through the 
hardpan to serve as outlets for the excess water that 
stands on the hardpans. Such holes, to be effective, 
should occur frequently, in which case the process 
becomes very expensive. 

27. Effect of gravel. — When the soil is underlaid 
with gravel, or if gravel seams pass through it within 10 
or 12 feet of the surface, the normal distribution of the 
soil moisture is disturbed. By such gravel is meant 
the loose, open gravel which makes the soil discontinuous. 
If gravel is mixed uniformly with the soil from the sur- 
face downward, or at varying depths, the soil may be 
looked upon as being continuous so far as the distribu- 
tion of water is concerned. 

When water, moving downward, reaches a layer of 
loose gravel, the descent of the moisture film is first 
arrested, then the film is thickened until the lower soil 
pores are filled, and, if irrigation is continued, gravita- 
tional water drips from the soil into the gravel below. 
The water which thus passes into the gravel can not move 
back by capillary means, and usually drains away into 
the subsoil and is lost to plant use. 

Soils, made faulty because of gravel seams, should 
therefore be irrigated lightly. Not enough water should 
be added to allow any part to move into the subsoil. 
Under such conditions, more frequent applications of 
water become necessary. On the benches and foothills, 
such soils are of frequent occurrence. 

28. Water table near surface. — When the standing- 
water table is within reach of plant-roots, heavy irriga- 
tion should be avoided. Just enough water should be 
added to keep the soil moist without allowing any appre- 
ciable quantity to drain into the ground water. 



SOIL AS WATER RESERVOIR 35 

29. Soil treatment. — A deep, continuous soil is the 
best under irrigated conditions. On such a soil enough 
water may be added at each irrigation to leave the top 
foot saturated after distribution has occurred. This 
quantity varies usually from a depth of 5 to 8 inches over 
the whole area. To make more rapid the entrance of 
water into the soil, the surface should be kept in a loose, 
absorptive condition. The deeper the soil is plowed, the 
greater the quantity of water that may be stored in a 
given time, in the top soil, to move gradually downward 
into the subsoil. Since the application of water tends to 
compact the soil, it becomes necessary to stir the soil 
between irrigations. Such stirring not only makes it 
easier for water to enter the soil; it also reduces the loss 
from evaporation. 

Soils, which within 10 or 12 feet from the surface are 
underlaid with hardpan or ground water, or made dis- 
continuous by gravel streaks or layers, must be irrigated 
cautiously. In such cases the quantity of water to be 
added should be such as to allow only a thin soil-mois- 
ture film to reach the hardpan, ground water or gravel. 
Small, frequent irrigations must be the rule in such cases 
— smaller and more frequent as the faults are nearer 
the surface. 

30. How much water can be stored. — It is clear from 
the statements of this chapter that water may be stored 
in soils to considerable depths as a film surrounding the 
soil particles and filling the capillary spaces. Since water, 
whether from rain or irrigation, is ordinarily applied 
intermittently, it is important to know how much of the 
water added at any one time is retained by soils for 
the use of plants. 

At the Utah Station, where most of the precipitation 



36 



IRRIGATION PRACTICE 



comes in winter, a long series of experiments showed 
conclusively that in the spring most of the water that 
fell throughout the winter was held in the upper 8 feet of 
soil. The quantity held in the soil section varied with 




Fig. 9. Penetration of roots of prune tree. 



SOIL AS WATER RESERVOIR 37 

the percentage of water in the soil in the fall. If the soil 
went into the winter in a dry condition, practically all 
of the winter precipitation was found in the spring in the 
upper 8 feet. If, on the other hand, the soil was well 
filled with water in the fall, from fallowing or fall irriga- 
tion, a relatively small quantity of the winter precipita- 
tion was found in the upper 8 feet of soil, when spring 
opened. In both cases the soils were saturated in the 
spring. That is, the upper foot was fully saturated; the 
percentage diminished steadily with each succeeding 
foot in accordance with the law of distribution already 
explained. It was clear that when the soil was fairly 
completely saturated in the fall, the winter precipitation 
soaked down below the 8-foot limit. During six years, 
1902 to 1907, the percentage of the total winter pre- 
cipitation found stored in the soils that went into the 
winter in the driest condition varied from 63 to 96 per 
cent. 

This teaches, incidentally that, when the soil is sat- 
urated to a depth of 10 to 12 feet, there is not an advan- 
tage in adding more water. Therefore, in districts where 
the precipitation comes in winter, early spring irrigations 
may have little value. On the other hand, where the 
winters are dry and the summers wet, early spring irriga- 
tions should prove very profitable. 

At the North Platte substation of the Nebraska 
Station, where the precipitation comes chiefly in early 
summer, a similar series of experiments were conducted. 
It was found that, in spite of the water-dissipating con- 
ditions of summer, from 40 to 50 per cent of the rain 
which fell from May 1 to September 1 was stored in the 
soil to a depth of 6 feet at the end of the period. Since it 
was evident that the water passed below the 6-foot limit, 



38 IRRIGATION PRACTICE 

it is probable that considerably more of the summer 
precipitation would actually have been found if moisture 
determinations had been made to greater depths. 

Similar results were obtained from the irrigation 
experiments of the Utah Station. Water was added in 
varying quantities to a deep loam soil already well filled 
with water. The soil was sampled to a depth of 8 feet 
twenty-four hours after irrigation. The results for one 
year follow: 

Depth of water applied, in inches . . . 2.5 5.0 7.5 

Per cent of the water added, found one 

day after irrigation 100.00 77.04 68.87 

Some of the water was no doubt lost by evaporation; 
some moved below the 8-foot limit, yet from 69 to 100 per 
cent of the total quantity added was found to be stored 
in the soil, for the use of plants, one day after irrigation. 

It is clear, therefore, that water, whether of rain or 
irrigation, may be stored in soils. In clay soils, with fine 
particles and a large surface, much more water may be 
stored than in sandy soils, with coarse particles and a 
small surface. If evaporation is prevented, and crops 
are not growing on the soils, such stored water may 
remain in the soil for long periods of time. If the water 
is in the film condition, there is no great downward 
movement after equilibrium is once restored. 

31. Absorption of water by soils. — Water storage is 
best accomplished when the water is made to enter the 
soil quickly. This happens when the top soil is kept in a 
loose condition and when the soil, to a depth of several 
feet, is tolerably moist. If the surface is hard, the run- 
off is large; if the soil is dry, the downward penetration 
is slow. 



SOIL AS WATER RESERVOIR 39 



REFERENCES 

Alway, F. J., and Clark. A Study of the Movement of Water 
in a Uniform Soil under Artificial Conditions. Nebraska Experi- 
ment Station, Twenty-fifth Annual Report, p. 246 (1912). 

Burr, W. W. Storing Moisture in the Soil. Nebraska Experiment 
Station, Bulletin No. 114 (1910). 

Leather, J. W. Water Requirements of Crops in India. Part II. 
Agricultural Research Institute, Pusa, Memoirs of the Depart- 
ment of Agriculture in India, Chemical Series, Vol. I, No. 10 
(1911). 

Loughridge, R. H. Distribution of Water in the Soil in Furrow 
Irrigation. United States Department of Agriculture, Office 
of Experiment Stations, Bulletin No. 203 (1908). 

Widtsoe, J. A. Dry-Farming (1911). Chapter VII, Storing Water 
in the Soil. 

Widtsoe, J. A. The Storage of Winter Precipitation in Soils. Utah 
Experiment Station, Bulletin No. 104 (1908). 

Widtsoe, J. A., and McLaughlin, W. W. The Movement of 
Water in Irrigated Soils. Utah Experiment Station, Bulletin 
No. 115 (1912). 



CHAPTER IV 
SAVING WATER BY CULTIVATION 

Water added to the soil by the natural precipitation 
or by irrigation is disposed of in two chief ways: One part 
runs off the land; another part soaks into the ground. 

The water which soaks into the soil may be disposed 
of in three ways: (1) Immediately after water has entered 
the soil, evaporation begins at the surface and, in time, 
if not checked, the water in the greater depths will be 
brought to the surface, to be returned to the air in the 
form of water vapor. (2) If an excess of water has been 
applied, another part sinks below the reach of the plant 
roots and may connect with the country drainage, and 
thus be lost to the farmer. (3) A part remains in the 
soil and supplies the plant with the water needed in its 
growth. 

The vital thing in irrigation practice is to bring the 
water into the soil properly and to keep it stored there, 
within reach of the roots, until it is needed by the plant. 

32. The run-off. — The run-off collects in hollows or 
cuts channels to connect it with the larger streams of 
surface water. The quantity of water thus lost often 
forms a very large part of the total water added by the 
natural precipitation or by irrigation. To prevent this, 
it is necessary to keep the top soil in a loose, open con- 
dition, so that the water that falls upon it may be 
absorbed quickly. Where the major part of the precipi- 
tation comes during the winter or spring, the best way of 

(40) 



SAVING WATER BY CULTIVATION 41 

accomplishing this is to plow the land in the fall and, 
unless fall crops are planted, to allow it to lie in a rough 
state throughout the winter. Where the precipitation 
comes largely during the summer and spring, it is much 
more difficult, because of the growing crops, to keep the 
top soil in a condition to absorb water readily. 

Much water is nearly always lost at the time of thaw- 
ing and melting snow. In such districts all furrows and 
rows of plants should be made to conform with the slope 
of the land. A furrow plowed up and down a gentle slope 
forms an admirable channel for the escape of water, while 
a furrow plowed at right angles to the slope tends to catch 
and to hold back the water which flows downward. 
This is also true with regard to planting. Drill culture 
is now the only acceptable method of planting; and it is 
always desirable, from the point of view of preventing the 
run-off, to plant the rows of crops at right angles to the 
general slope of the land. Each row then tends to pre- 
vent excessive run-off. 

In irrigation, the loss due to run-off is frequently a 
very serious matter. When water is applied by the 
flooding method, it is relatively easy to control the run- 
off by building dikes around the field. In fact, some kind 
of diking is usually thrown up around large fields, when- 
ever water is applied by the flooding method. The vari- 
ous systems of irrigation by flooding differ chiefly in the 
means devised for preventing the surface loss of water. 
If no diking is used, the lower end of the field is usually 
crossed by a ditch, which receives the waste water and 
carries it to some other field. 

In the furrow method of irrigation it is very difficult, 
if not impossible, to prevent wholly the run-off. By the 
furrow method, water is usually applied at one end of the 



42 IRRIGATION PRACTICE 

field and allowed to run down long furrows, often several 
feet apart. It is practically impossible so to regulate the 
stream that all the water is absorbed just at the end of 
each furrow. In fact, if this is attempted by using a very 
small stream, it means that the upper end will receive a 
very large quantity of water, while the lower end will be 
relatively dry and often without a sufficient supply of 
moisture for abundant plant-growth. If a large stream is 
used, the whole furrow is given a thorough wetting, but a 
large quantity of water is wasted at the end of the furrow. 
This waste water is usually received by a transverse ditch 
and used on some lower field. To reduce the run-off and, 
at the same time, give each furrow a sufficient irrigation, 
the best plan seems to be to use a small stream and a 
rather short furrow, repeating the furrow below as many 
times as may be necessary. The shorter the furrow is, 
the more thoroughly and uniformly may water be applied 
to the soil. 

In any event, the run-off water must be carefully and 
skilfully used on lower fields. The run-off presents a 
problem which must be solved in its own peculiar way on 
each individual farm. No general rules can be laid down 
for using the run-off, since the layout of one farm is 
generally different from that of any other. 

33. The upward movement of water. — Under methods 
of irrigation that use water in moderation, very little 
water drains below the zone of root-action, yet under 
the most favorable conditions water may move upward 
and be lost from the soil surface. The movement of 
water is usually from the thick to the thin film, that is, 
from the moister to the drier parts of the soil. When, 
therefore, a soil dries at the surface, there is a steady 
upward movement of water from particle to particle to 



SAVING WATER BY CULTIVATION 43 

supply that lost by evaporation at the top and to place 
the remaining water in full equilibrium with all active 
forces. Such loss of water is felt to the full depth of soil 
concerned in plant-growth. 

As evaporation proceeds from the top soil, the water 
in every soil layer diminishes to the full depth of root- 
action. The process may be likened roughly to the behav- 
ior of cotton packed loosely in a box. If a small quantity 
is removed from the top, the remainder expands and 
fills the box again, the difference being that the whole 
mass is looser from the top downward than it was before. 
So, after evaporation has occurred, and water has moved 
upward to replace the loss, there is a thinner soil-water 
film throughout the soil. This process may go on until 
the soil-water film has been reduced to the minimum 
thickness that allows capillary movement. When this 
degree of dryness has been reached, it does not follow that 
the film is of the same thickness at every point to the full 
depth involved. On the contrary, the lower layers, to a 
depth of 8 to 10 feet, contain more water than do the 
upper soil layers. At first, as evaporation proceeds, the 
tendency is to distribute the water evenly over the soil 
sections below the upper one, which is immediately 
exposed to the atmosphere and therefore always drier. 
As the lento-capillary point is approached, the upward 
movement becomes more and more sluggish; and, in 
fact, it is ordinarily very difficult to reduce the lower 
soil layers below this point, though the upper layers may 
be brought considerably lower in their moisture content. 
When living plant-roots fill the soil, this distribution 
does not hold, for the roots draw moisture directly from 
the soil, and the percentage of soil moisture is in inverse 
proportion to the distribution of the roots. 



44 



IRRIGATION PRACTICE 



To stop the upward movement of soil water due to 
surface evaporation is a chief consideration of a system 
of irrigation-farming in which economy in the use of 
water is a vital factor. 

34. Intensity of evaporation. — It is well known that 
water evaporates into the air whenever the air is not 
fully saturated with water vapor. Under the conditions 



-I 

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xJhn. Feb. Mar /7p/r -May t/vne Jis/y rfv# Sept. Oct A/ov'. /)ee. 



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■ 'pemr; h/re 



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80 



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4o 



Fig. 10. Evaporation usually exceeds rainfall. 



prevailing over the earth's surface, the air is always 
unsaturated. In arid regions the air is very dry, as is 
well shown by the high heat that may be endured in 
such places, due to the rapid evaporation of perspiration 
into the dry air. 

The rate of evaporation from water surfaces is much 
larger than commonly believed. Briggs and Belz have 
sought out all available records in various sections of the 
United States, of the quantities of water that will evapo- 
rate from a free-water surface during the six summer 
months, April to September inclusive. A summary of 
their findings is presented in the following table: 



SAVING WATER BY CULTIVATION 



45 



Water Lost (in Inches) by Evaporation from a Free-Water 
Surface from April to September, Inclusive 



State 


Highest 


Lowest 




56.2 
71.8 
61.6 
51.0 
54.6 
42.0 
27.6 
39.4 

59.9 
32.1 
32.6 
41.3 
31.4 
38.0 
54.6 
28.8 

28.6 
29.5 
26.7 
24.6 


54.2 


California 


21.2 


Nevada 


29.3 
39.9 


New Mexico 


40.1 


Utah 


30.7 


Kansas 


45.2 


North Dakota 


30.2 

34.8 
29.8 


South Dakota .....' 


33.7 


Texas 


45.7 


Massachusetts 


26.9 

25.8 


New Jersey 




New York 




Ohio 









This table is not complete, but it shows unmistak- 
ably, first, that evaporation is much greater in the arid 
than in the humid region, and, second, that in both 
humid and arid regions the evaporation from a free-water 
surface, during the six summer months, is considerably 
more than the total quantity of irrigation water that 
should properly be applied in any one year. In the arid 
states, as, for instance, California, with its high evapora- 
tion record of nearly 72 inches, several times the quantity 
of water that should be applied in irrigation may easily 
be evaporated into the air during the growing season. 

From soils kept wet at the surface, evaporation goes 
on even faster than from a water surface. For instance, 



46 IRRIGATION PRACTICE 

Fortier reports an average weekly evaporation from a 
wet soil of 4.75 inches and from a water surface placed 
under like conditions only 1.88 inches — two and one-half 
times as much. The explanation of this must of course 
be sought in the higher temperature of the soil due to a 
lower specific heat and a higher absorptive capacity 
for heat. 

This strong tendency of water to return to the air 
by way of evaporation makes it fundamentally impor- 
tant to devise and put into operation methods that will 
prevent, to the largest possible degree, this form of the dis- 
sipation of water. (Fig. 10.) 

35. Conditions determining evaporation. — Many fac- 
tors are concerned in the evaporation of water from the 
surface of water or any moist substance such as an irri- 
gated soil. These may be classified as follows: 

1. Nature of soil. 

(a) Physical. 
(6) Chemical. 

(c) Depth. 

2. Meteorological conditions. 

(a) Temperature. 

(6) Sunshine. 

(c)" Relative humidity. 

(d) Winds. 

(e) Showers. 

3. Initial percentage of water. 

4. Condition of top soil. 

(a) Plowing. 
(6) Cultivation. 

(c) Rolling. 

(d) Packing 



SAVING WATER BY CULTIVATION 47 

The nature of the soil is of considerable importance. 
The finer the texture of the soil, the more rapidly does 
the water move upward to be changed into vapor. The 
darker the color of the soil, the more rapid the evapora- 
tion; for dark-colored soils absorb the heat of the sun- 
shine much more quickly than do lighter-colored ones 
such as characterize the arid region. The richer the soil 
is in soluble salts, the slower is the evaporation of water 
into the air. For that reason, evaporation from alkali 
lands is slow. The rate of evaporation is more rapid 
from a deep than from a shallow soil, for a given loss of 
water does not so greatly reduce the percentage of mois- 
ture in a deep as in a shallow soil. 

Meteorological conditions determine very largely 
the rate of evaporation of water from soils. Of these, 
temperature is most important. The higher the tempera- 
ture, the more rapid is the conversion of water into water 
vapor. Of almost equal importance is the intensity and 
quantity of sunshine. Much more water is lost from a 
wet soil on a sunny day than on a cloudy one. Shade is 
extremely effective in checking evaporation. In the Utah 
work, a saving of 25 per cent of the water evaporated 
was effected when the soil was shaded; and, in all proba- 
bility, as the temperature is very much lower in the 
shade, an even higher degree of saving may be effected. 
Frequently, a high temperature and much sunshine go 
together, so that their effects are felt at the same time. 
The drier the air, the more rapidly will the air take up 
water vapor. In the arid region, the relative humidity 
of the air is low, and evaporation goes on, as has been 
shown, much more rapidly than in humid sections. 
Winds, likewise, exert a strong drying effect on soils, 
especially in districts where the air is relatively dry. The 



48 



IRRIGATION PRACTICE 



water, as it evaporates from the soil, saturates the air 
immediately above the soil surface; and thus evapora- 
tion is diminished. Winds remove this layer of saturated 
air, and the rate of evaporation is increased. Summer 
showers, likewise, by establishing capillary connection 
with the lower soil layers, hasten evaporation. 

Finally, the wetter the soil is at the surface, the more 
rapidly is water evaporated from it. This vitally impor- 























































































































































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Jan feb Mar Apr May JuneJuly Aug SeptOct Nov'Dec.Jpn Feb Mar Apr May JuneJuly Aug SeptOct No* Dec ™ 

1904 1905 

Fig. 11. Relation beween temperature and evaporation (Tulare, Calif.). 

tant principle was observed in the Utah work, and has 
been confirmed by Whitney and Cameron and by For- 
tier. This law of the initial percentage declares that the 
evaporation of water from a soil surface varies as the 
initial percentage of soil moisture, — that is, the mois- 
ture at the beginning of the test. 

The three most important factors in determining the 
evaporation of water from a soil are undoubtedly the 
average temperature, the relative humidity of the air, 
the wind, and the percentage of water held by the soil. 



SAVING WATER BY CULTIVATION 49 

The temperature cannot be controlled, effectively, by the 
farmer; neither can the relative humidity; and, if the land 
is to produce the largest and best crops, there must be in 
the soil a fair abundance of water. To diminish the rate 
of evaporation by controlling these three factors seems, 
therefore, almost hopeless. The control must come from 
the proper treatment of the top soil. (Fig. 11.) 

36. Mulching to check evaporation. — It was observed 
many years ago, that evaporation of water from soils 
may be quite effectively stopped by covering the soil 
loosely with straw, manure, litter of any kind or loose 
soil. This method has been tried out practically in so 
many countries and by so many investigators that there 
can be no question about its effectiveness. 

Fortier recently re-examined the matter, under the 
climatic conditions of the irrigated sections of the United 
States, and found that a covering of sand, if of proper 
depth, applied to the soil immediately after irrigation, 
could be made to reduce the evaporation to less than 2 
per cent of the water applied. In earlier days, it was 
advocated rather largely that straw and other litters be 
placed upon the soil to prevent evaporation. This method, 
however, is too expensive to be of wide application. 

The method of today is to stir the top soil with proper 
implements. The process is called cultivation. The 
layer of loose dirt which is thus left upon the soil hinders 
very effectively the movement of soil water into the 
atmosphere. In the Utah work it was found that, by 
cultivation, an infertile clay soil lost only 63 per cent of 
the quantity lost by the non-cultivated soil; a fertile 
clay loam, 13 per cent, and a loose sandy soil, 34 per cent. 
Fortier found that by thorough cultivation of a southern 
California soil the loss by evaporation could be reduced 

D 



50 IRRIGATION PRACTICE 

to less than half of that from a non-cultivated soil. Scores 
of other investigators have demonstrated that the mulch 
formed by cultivation reduces largely the evaporation. 

This saving, due to mulching, is easily understood. 
As has been explained, soil moisture is held as a film 
around the soil particles. Water moving toward the soil 
surface must pass from particle to particle through the 
narrow films at the points of contact of the soil particles. 
The smaller or the fewer these points of contact, the more 
difficult is the upward movement of the water. If water 
were passing through a large tube into several smaller 
tubes, the flow of water would be retarded. When the top 
soil is loosened, the points of contact between the loose soil 
above and the compacted soil below become reduced. 
At the zone of loose earth, the ascending water finds it 
difficult to pass through the fewer points of contact, and 
at the same time to maintain its rate of flow. The more 
thoroughly the soil is cultivated, that is, the fewer the 
points of contact, the more difficult will the movement 
become, and the more greatly will the evaporation 
be reduced* 

Likewise, as a soil becomes dry, the flow of moisture 
through it is lessened. This is clearly understood when it 
is recalled that a dry soil means a soil with very thin 
moisture films around the particles. Water passing 
through thin films encounters much friction, and the 
rate of flow is diminished. Stirring the top soil tends to 
dry it out very rapidly, and to leave a very dry mulch, 
through which water can pass only with difficulty. Culti- 
vation, therefore, retards evaporation by breaking the 
points of contact between the upper and lower soil layers 
and by drying out the loosened top layer. 

It is true that from the surface of every soil particle, 



SAVING WATER BY CULTIVATION 



51 



at any depth, water is evaporated, until, if the soil is 
moist, the pores of the soil are filled with air saturated 
with vapor water. This saturated soil air moves, how- 
ever, very slowly into the atmosphere. Buckingham 
has shown that water vapor escapes from the soil air 
only by the slow process of diffusion; that is, the particles 
of water vapor find their way, one by one, into the atmos- 
phere, while there is a corresponding movement of 
atmospheric gases into the soil air. This interchange of 
gases between the soil air and the atmosphere is so small 
as to be of little or no consequence in the loss of soil water 




Fig. 12. Evaporation losses from soils protected with mulches of different depths. 

by evaporation. Practically all soil water is lost by evap- 
oration at the soil surface. 

Buckingham has shown, also, that very little water 
is lost by direct evaporation 2 inches below the surface. 
From below a 12-inch layer of dry soil the evaporation- 



52 IRRIGATION PRACTICE 

loss is insignificant, amounting at most to only 1 inch of 
rainfall in six years. 

The most effective method of checking evaporation 
from the soil is to stir the top soil thoroughly with any 
one of the many kinds of cultivators now found on the 
market and built especially for the purpose. (Fig. 12.) 

37. Self -mulching soils. — Under arid conditions, 
some soils possess a self-mulching power. The abundant 
sunshine, high temperature and low relative humidity 
of arid sections, cause a very rapid evaporation. After 
an irrigation on a very hot summer day the top soil may 
be dried out so rapidly that the lower soil layers cannot 
send moisture upward in time to supply the loss. Under 
such conditions the evaporation is automatically 
decreased. The dry top soil, thus induced, is an effec- 
tive check upon the upward movement of water. This 
may be one explanation of the fact that in many virgin 
arid lands much of the rainfall remains stored for months 
at a time. Added to this is another condition of frequent 
occurrence. Arid soils are, as a rule, rich in lime. In some 
cases the calcareous substances of arid soils make up one- 
fourth to one-half of the soil itself. Such soils, as they 
dry out, become loose. It frequently happens, there- 
fore, that when such a soil, after an irrigation, is dried 
out by rapid evaporation, the surface layer falls into a 
natural mulch which is fairly effective in stopping evapo- 
ration. Buckingham reports an interesting experiment, 
in which he found that the rapid evaporation due to arid 
conditions so dried out the top soil that the loss of water 
in a year was only 11.2 inches as against 51.6 inches from 
a similar soil under humid conditions which permitted a 
slow but steady evaporation. 

The stirring of such self-mulching soils does not always 



SAVING WATER BY CULTIVATION 53 

save soil moisture. In the Utah work such a soil was 
found, from which one and one-half times more water 
was lost during the growing season when cultivation was 
practised. The natural mulching of this soil permitted 
the lowest evaporation of a large series of tests with 
several varieties of soil. Nevertheless, even on such soil, 
the stirring of the soil carried with it other beneficial 
results of high value to crops. That is, even though 
cultivation on such soils may cause a greater loss of water, 
the soil becomes able by the cultivation to produce more 
dry matter with the water actually at its disposal. This 
was well brought out in the Utah work, for the self- 
mulching soil produced a crop 14 per cent larger on the 
cultivated areas. 

Self-mulching soils are not plentiful, and too much 
reliance should not be placed upon them. The irrigation 
farmer is safe only when he cultivates his soils thoroughly 
and frequently throughout the season. 

38. Time of cultivation. — The rate at which water 
soaks into a soil depends largely upon the physical con- 
dition of the land. If the soil is coarse and loose, the down- 
ward movement is rapid; if fine and compact, the down- 
ward movement is slow. In any case the top soil remains 
saturated or too wet for cultivation during several hours, 
or days, after an irrigation. A sand or loam soil may often 
be cultivated within one or two days after irrigation; but, 
on a clay soil, this cannot be done until three to seven 
days after irrigation. During this period before cultiva- 
tion, when the top soil remains moist, evaporation losses 
occur very rapidly. In fact, from one-fifth to one-third 
of the loss due to evaporation throughout a three- or 
four-week period occurs before the cultivator can be 
applied to form a protective soil mulch. 



54 IRRIGATION PRACTICE 

The chief protection against the great losses immedi- 
ately after irrigation and before cultivation is possible, 
is a loose, spongy top soil that absorbs the water the 
moment it is applied and permits it to soak deeply into 
the soil away from the immediate action of the sun's 
rays. Occasionally it may be profitable to scatter a 
mulch of some kind over the soil, immediately after an 
irrigation, but this is of extremely limited application. 
If water is applied by sub-surface methods this pre- 
cultivation loss may be prevented, but sub-irrigation is 
seldom profitable except in districts were natural sub- 
irrigation is feasible. 

The soil should be cultivated just as soon as it is pos- 
sible to do so after an irrigation, without doing injury to 
the soil. If cultivation is performed too soon after irriga- 
tion there is danger of leaving the top soil puddled or 
in an otherwise undesirable physical condition for plant- 
growth. By too early cultivation a soil may be perma- 
nently injured for the season or even for several seasons. 
The farmer who cultivates too early, and thereby leaves 
the top soil in a poor physical condition, ultimately loses 
more than does he who permits evaporation to go on a 
day longer, to make sure that the soil is in the right con- 
dition for cultivation. Whenever the soil is dry enough 
to support the man and horse with the cultivating tool, 
it is usually safe to begin cultivation. 

On the other hand, it must be said that, in the great 
majority of cases, the farmer permits evaporation to go 
on many days after the time of safe cultivation has been 
reached. Few fields are injured from too early cultiva- 
tion. Over the whole irrigated area, the farmers have 
looked upon cultivation as an incidental matter, because 
they have not realized the tremendously large quanti- 



SAVING WATER BY CULTIVATION 



55 



ties of water that may be lost from the soil by evapora- 
tion. The magnitude of such losses is well shown in the 
following typical results taken from the Utah work. The 
soil at the beginning of each test contained practically 
17.5 per cent of water. 



Days after irrigation 


Pounds of water 

lost per' 

square foot 


Tons of water 
lost per acre 


Loss as depth 

of water in 

inches 


One to fourteen 

One to twenty-one .... 


7.54 
10.08 
14.09 


164.22 
219.54 
307.09 


1.45 
1.93 
2.71 



During the first seven days after irrigation, a quan- 
tity of water equivalent to nearly 1.5 inches was lifted 
from the soil by the power of the sunshine; during the 
first fourteen days, nearly 2 inches, and, during the first 
twenty-one days about 2% inches. Fortier and Beckett 
found that during a twenty-eight-day period after irri- 
gation a non-cultivated soil lost 2.13 inches of water, of 
which about .8 of an inch or nearly 40 per cent was lost 
during the first three days after irrigation, before culti- 
vation could begin. Such great losses in an arid section 
justify every effort of the farmer to conserve the soil 
moisture by cultivation, — and it should be done as early 
as possible so that the water saving may be large. 

39. Depth of cultivation. — The depth to which a soil 
is cultivated, that is, the thickness of the soil mulch 
produced, determines the rate of evaporation and there- 
fore the quantity of soil moisture that may be saved. 
This is only to be expected, for the thicker the dry mulch 
above the moist soil from which evaporation proceeds, 
the greater is the hindrance offered to the diffusion of 



56 



IRRIGATION PRACTICE 



water vapor into the atmosphere, and the less effectively 
can the sunshine heat the evaporating surface. The 
best investigations on this subject are those recently 
conducted by Fortier, and Fortier and Beckett, under 
true arid conditions. These experiments were made at 
five different points in the arid region — in California, 
Montana, Nevada, Washington and New Mexico — so that 
the validity of the results could be checked under the 
varying climatic conditions of the irrigated region. 
Immediately after each irrigation, "fine, dry, granu- 
lated soil mulches," of different depths, were placed upon 
the soil, and the water losses were determined during a 
period of four weeks. Some of the average results are 
as follows: 



Depth of mulch in 
inches 


Loss of water 

during 28 days 

in inches 


Per cent 


None 
3 
6 
9 


1.75 
0.78 
0.34 
0.22 


100.0 
42.3 
19.4 
12.5 



The thicker the mulch placed upon the soil the smaller 
was the evaporation, varying from 1.75 inches, when no 
mulch was applied, to .22 inch or 12.5 per cent, when a 
9-inch mulch was spread over the soil surface. 

In another series of experiments, a 10-inch mulch 
practically stopped evaporation. When the mulch is 
made by cultivation, similar results are obtained, the 
difference being the loss immediately after irrigation 
and just before cultivation, discussed above. 

It may be said safely that the deepest cultivation is 
the most effective for the checking of evaporation from 



58 IRRIGATION PRACTICE 

irrigated soils. However, in practice it is often difficult 
to cultivate below a depth of approximately 6 inches, 
unless the soil is of the right character and proper imple-. 
ments are used. The greatest depth to which any soil 
may be cultivated must be determined by the individual 
farmer. There has been considerable opposition to deep 
cultivation on the ground that it tends to destroy the 
roots which feed in the upper layers of the soil. Some 
plants are naturally more shallow-rooted than are others, 
but an important thing in all arid agriculture is to com- 
pel plant-roots to go deeply into the soil. Shallow-rooted 
plants, under conditions of irrigation, usually indicate 
that the farmer has used water unwisely by irrigating 
too frequently or too heavily. Proper irrigation, moderate 
in quantity and at proper intervals, causes practically 
all the ordinary cultivated plants to strike their roots 
deeply into the soil — so deeply that no damage results 
from the deep cultivation indicated by the experiments 
here recorded. In many sections of the West, notably 
in the orange districts of southern California, where the 
rainfall is light and irrigation water scarce, deep culti- 
vation has become a general practice in spite of the 
general belief that citrous trees are shallow-rooted. 
Before a rational irrigation practice is firmly established, 
farmers must become convinced that there is no harm 
whatever in cultivating deeply and as soon as possible 
after each irrigation. 

40. Frequency of cultivation. — Few experiments have 
been conducted on this subject, but the principles already 
laid down give a fairly clear indication of the cultivations 
a field should receive throughout the season. Even after 
a thorough cultivation, most soils gradually settle into a 
more compact mass. In some soils this settling is so great 



SAVING WATER BY CULTIVATION 59 

that it re-establishes capillary connections between the 
mulch and the moist soil below, and evaporation is then 
resumed. Such soils, which are soon recognized, should 
be cultivated several times between each irrigation. When 
soils show no such tendency to settle, it may be sufficient 
to give them one good cultivation after each irrigation. 
Generally, it is well to cultivate the soil at least once 
every three weeks throughout the irrigating season and a 
bi-weekly cultivation is probably better. 

Summer showers also determine the frequency of 
irrigation. A summer shower, unless it is very light, 
beats down the the mulch and usually saturates the soil 
sufficiently to establish vigorous capillary communica- 
tion with the lower soil layers. This condition may lead 
in a few hours to large evaporation losses. For that 
reason, every summer shower should be followed, as soon 
as the soil is dry enough, with a thorough cultivation. 
Where the precipitation comes chiefly in the fall, winter 
or spring, the summers are relatively dry and the few 
light summer showers may easily be followed by the 
cultivator; but, where the winter is relatively dry and the 
precipitation comes chiefly in early or midsummer, the 
rains are often so frequent and heavy that to follow them 
with cultivators is difficult, if not practically impossible. 
True, under such conditions, the water necessary in irri- 
gation is relatively smaller, so that evaporation losses 
can better be sustained there than in districts of dry 
summers, where the annual precipitation is also usually 
low. Wherever possible, however, cultivation should 
follow both summer shower or rain and irrigation. 

41. Cultivation and soil fertility. — So much has been 
said concerning the value of cultivation in the conserva- 
tion of soil moisture that one may be led to believe that 



60 IRRIGATION PRACTICE 

the whole virtue of cultivation lies therein. However, cul- 
tivation has other beneficial effects quite as important as 
the direct saving of soil moisture. The loosening of the 
top soil permits the entrance of the atmosphere, with 
the free exchange of gases between the atmosphere and 
the soil air, which ventilates the soil and enables various 
physical, chemical and biological changes to take place. 
The result is of the highest importance to plant life. The 
condition of the top soil, the part turned by the plow and 
stirred by the cultivator^ is of first importance in all 
agriculture. A striking illustration of this other value 
of cultivation was secured in the Utah work. In a series 
of tests designed to show the moisture-saving possibili- 
ties of cultivation, a very careful account was kept of the 
total yield of dry matter produced under the various soil 
treatments. Corn was grown on four different soils vary-* 
ing from a coarse sand to a fine clay, and from high fer- 
tility to great infertility. The following are some of the 
results obtained: 

Pounds of Water Transpired for One Pound of Dry Matter 



Infertile sand . . . 
Fertile sandy loam 
Fertile clayey loam 
Infertile clay . . . 



Not cultivated 


Cultivated 


454 


732 


603 


252 


535 


428 


753 


582 



In every case, excepting the abnormal infertile sand, 
the careful stirring of the soil enabled the plant to pro- 
duce one pound of dry matter with a smaller quantity 
of water than when the soil was not cultivated. The 
sandy loam was of a self-mulching nature, and really 
lost water by cultivation, yet on this soil, also, cultiva- 



62 IRRIGATION PRACTICE 

tion enabled the plant to produce dry matter at a smaller 
water cost. 

Cultivation of the soil, therefore, prevents the waste 
of water by evaporation, and induces soil changes that 
enable the crops to produce larger yields with a given 
quantity of water. In truth, cultivation may take the 
place of irrigation. 

42. Rolling. — Rolling is the opposite of cultivation. 
It compacts the top soil. As a result, excellent capillary 
connections are established between the top and the sub- 
soil and water is enabled to move upward, rapidly, from 
the lower layers to the surface, there to be evaporated 
into the air. There is no more dangerous practice than 
this, if evaporation of soil moisture is to be prevented. 
Moreover, a soil which has been compacted by rolling 
offers much resistance to the entrance and downward 
movement of water. Rolling, therefore, (1) prevents the 
water from entering the soil easily, and (2) allows the 
water which does enter the soil to evaporate rapidly. 
From the point of view of water-conservation it is an 
extremely wasteful process. 

In a few special cases rolling may be permitted in a 
good system of irrigation agriculture. For instance, in 
raising sugar beets for factories, the soil is carefully rolled 
after the planting of the seed, chiefly to insure good 
germination. This, however, is not necessary except in 
districts where the spring precipitation is light or where 
the soils have been so handled as to be too dry for satis- 
factory germination. By proper methods of fall plowing 
this precaution would probably be unnecessary. 

A special phase of rolling may be of importance. 
Campbell recommends highly a sub-surface packer, 
designed to pack the soil at the bottom of the plow fur- 



SAVING WATER BY CULTIVATION 63 

row while it leaves the top soil loose and open. The merit 
in this process is that the loose top soil permits the easy 
entrance of water into the soil and also acts as a mulch 
to prevent evaporation. To accomplish such sub-sur- 
face packing the Campbell machine may be used, or the 
soil may be thoroughly cross-disked. 

Rolling, whether on top or below the surface, is of 
small and questionable value in any system of irriga- 
tion practice. 

REFERENCES 

Briggs, Lyman J., and Belz, J. O. Dry-Farming in Relation to 

Rainfall and Evaporation. United States Bureau of Plant 

Industry, Bulletin No. 188 (1911). 
Buckingham, Edgar. Contributions to Our Knowledge of the 

Aeration of Soils. United States Bureau of Soils, Bulletin 

No. 25 (1904). 
Buckingham, Edgar. Studies on the Movement of Soil Moisture. 

United States Bureau of Soils, BuUetin No. 38 (1907). 
Fortier, Samuel. Evaporation Losses in Irrigation and Water 

Requirements of Crops. United States Office of Experiment 

Stations, Bulletin No. 177 (1907). 
Fortier, Samuel, and Beckett, S. H. Evaporation from Irrigated 

Soils. United States Office of Experiment Stations, Bulletin 

No. 248 (1912). 
Whitney, Milton, and Cameron, F. K. Investigations in Soil 

Fertility. United States Bureau of Soils, Bulletin No. 23 (1904). 
Widtsoe, J. A. Factors Influencing Evaporation and Transpira- 
tion. Utah Experiment Station, Bulletin No. 105 (1909). 
Widtsoe, J. A., and McLaughlin, W. W. The Movement of W'ater 

in Irrigated Soils. Utah Experiment Station, Bulletin No. 115 

(1912). 
Widtsoe, J. A. Dry-Farming. Chapter VIII (1911). 



CHAPTER V 

SOIL CHANGES DUE TO IRRIGATION WATER 

The soil cannot, directly, be greatly changed by the 
farmer. As it is, so, in a large measure, it must remain. 
Tillage implements modify only slightly the upper layer 
of the soil. Water, however, may cause fairly large 
changes in the soil to the full depth to which it pene- 
trates. Irrigation, therefore, with its power of regula- 
ting the quantity of water applied, may be made a means 
of modifying soil properties. Physical, chemical and 
biological soil changes are induced by irrigation, and 
some of the most important principles of a permanent 
system of irrigation agriculture, depend upon the effects 
of water upon soil. 

43. Contraction and moisture film. — If a camel's-hair 
brush be dipped in water, and then removed, the hairs 
cling together to form a narrow and rather hard brush 
suitable for use in painting. If a trifle of the water in the 
brush be squeezed out, the brush becomes rather stiffer 
than it was before, but if more water be removed, the 
brush become looser and looser until it is dry and fluffy. 
This adhesion of the hairs is due (1) to the contraction 
of the films surrounding each little hair, and (2) to the 
contraction of the water film enveloping the whole brush. 
(Fig. 15.) 

In like manner, the particles of a soil, when wetted or 
dried, tend to move either more closely together or farther 
apart, and the soil becomes more or less rigid. When 

(64) 



SOIL CHANGES DUE TO IRRIGATION 



65 



water is applied to a soil it forms a film around each of 
the particles of widely differing sizes; and further, many 
small and large particles may form a larger composite 
particle or crumb with one continuous film surrounding 
it. The soil should possess a well-devel- 
oped crumb structure; for the plant has 
then a better chance to develop than if 
the individual particles remain separate 
in single-grain structure. 

44. Cohesion of soil particles. — By 
direct examination, every good farmer 
may determine whether the soil is in 
proper condition for plowing or for other 
cultural operations. Usually this condi- 
tion means that the proportion of mois- 
ture in the soil is such that a plow or a 
cultivator may be passed through it with 
the least resistance and without destroy- 
ing the crumb structure or tilth. The 
question of the force with which dry or 
moist soil particles stick to each other is 
not of itself of very great importance; fig. is. Adhesion of 
but it is of interest in showing the effect hairs due to water ' 
of various proportions of water on the properties of the 
different soils. Pure clay dries to a very hard mass, 
difficult to break. If to the clay be added sand, humus, 
gypsum or lime, the resulting mass, when dry, may be 
broken with less than one-fifteenth the force necessary 
to break the pure clay. In fact, coarse sands or soils rich 
in gypsum or lime, as they dry, often fall apart into a 
coarse mass, which forms a natural mulch over the soil. 

The force with which soil particles are held together 
depends, primarily, upon three factors: (1) the physical 

E 




66 IRRIGATION PRACTICE 

constitution of the soil; (2) the water content, and (3) 
the presence of various salts. The finer the soil is, the 
more firmly the dry particles are held together. As the 
soil water increases, clay is less firmly, and sand more 
firmly, held together. The presence of soluble salts 
tends, in general, to reduce the force with which soil par- 
ticles stick together, though lime and other substances 
have the opposite effect. 

Of chief importance to the irrigation farmer is the 
knowledge of how varying amounts of water affect the 
cohesion of soil particles, since it is within his power to 
regulate the quantity of water in the soil. Cameron and 
Gallagher have done some excellent work on this subject. 
They concerned themselves only with the percentages of 
soil water which are found in actual agricultural practice; 
for, large additions of water, beyond the saturation point 
of the soil, always cause the soil crumbs to fall apart into 
their constituent particles; and, likewise, at moisture 
contents below the wilting point, the cohesive powers of 
the soil grains have little agricultural meaning. 

Sand, loam, clay and humus soils were studied. In 
all of these, save the clay, as the soil moisture increased, 
the force with which the soil crumbs were held together 
at first decreased up to a definite point, then increased, 
and, by the addition of more water, decreased again to 
the point of minimum cohesion. In other words, as water 
is added to a dry soil, the soil first gradually softens; then 
gradually hardens ; then rapidly softens until it is a mushy 
mass. The point of low cohesion, or easy penetration at 
which tillage implements may be passed through the soil 
with small resistance, corresponded, generally, with the 
so-called point of optimum water content in the soil; 
that is, the degree of wetness at which, according to the 



SOIL CHANGES DUE TO IRRIGATION 67 

judgment of experienced tillers of the soil, the soil is in 
the best condition for plant-growth. In the case of the 
clay soil, as more water was applied, the force of cohesion 
continued steadily to diminish, with no definite point at 
which a temporary hardening occurred. At a definite 
degree of wetness, however, the clay soil is in the best 
condition for working and for plant-growth. This is in 
full harmony with the known properties of clay. 

The point of optimum water content is, approxi- 
mately, identical with the field water capacity discussed 
in Chapter II. It seems clear that, when the soil contains 
a medium amount of water, that is, a quantity lying 
between the maximum water capacity and the point of 
lento-capillarity, it can be most easily worked, and is in 
best condition for plants. It is interesting to note how this 
intermediate point continually appears in the study of 
the relation of soils and plants to varying water content. 

45. Volume changes of soils. — It follows that, if such 
differences in the force with which the soil crumbs are 
held together are induced by the application of varying 
quantities of water, the soil particles themselves must 
actually move and rearrange themselves, as water is 
added to or removed from the soil. Such movements of 
the soil particles would naturally cause, also, correspond- 
ing changes in the volume of the soil. This is an estab- 
lished fact, well known to every practical farmer. If 
wet clay is allowed to dry it shrinks, with the formation 
of large cracks in the ground. When water is again added, 
the clay swells and the cracks largely disappear. In a 
large measure, this is true of all agricultural soils. As they 
receive water, they swell; as they dry, they contract. 

The changes in the soil volume, due to the addition 
of water, are very great. In clay and humus soils they 



68 



IRRIGATION PRACTICE 



are often as high as 50 to 75 per cent of the original 
volume; with average soils, receiving moderate quanti- 
ties of water within the limits of practical agriculture, 
the volume changes are from 7 to 12 per cent of the 
original volume. Such fairly large variations, occurring 
over acres of land, represent great total changes, capable 
of modifying deeply the character of the soil. 

The reason for such volume changes is simple. In a 
dry soil the particles, lying rather closely side by side, 
occupy a relatively small space. When water is added, 
the soil particles group themselves into larger loose aggre- 
gates or crumbs, which occupy more space. There is a 




Fig. 16. Cracked river sediments showing volume changes due to water 



continuous arrangement and rearrangement of soil parti- 
cles, and a corresponding variation in the soil volume as 
the percentage of water in the soil changes. 

Cameron and Gallagher found that, as water is added 
to the soil, the volume becomes larger and larger, until a 
certain definite point is reached, after which the volume 



SOIL CHANGES DUE TO IRRIGATION 69 

becomes smaller and smaller. This point of largest vol- 
ume coincides almost exactly with the point at which the 
penetration of the soil is easy; which, as has been said, 
is the point of optimum water content. The farmer who 
desires to keep the soil in the best tilth, from top to lower 
depths, in order to increase the air space in the soil and 
to permit the easy penetration of roots, can do so by main- 
taining in the soil a moderate quantity of water, between 
the point of lento-capillarity and maximum capacity, 
somewhere in the neighborhood of the field capacity. 
The farmer who depends upon the rainfall and, therefore, 
cannot control his water supply, cannot well maintain 
the soil in this good condition. The irrigation farmer, on 
the other hand, who may, usually, apply water at will, 
can so plan his irrigation, when he knows his soil, as to 
maintain the land during the larger part of the season 
in the most desirable condition for plant-growth. (Fig. 16.) 

46. Effect on top soil. — Through the top soil, whether 
under irrigation or rainfall, all water added to a soil 
ordinarily passes. The top soil first becomes completely 
saturated, then it dries out quite thoroughly, and the 
process is frequently repeated. It follows, therefore, that 
the top soil is subject, almost from day to day, to the 
greatest changes, physical, chemical and bacteriological. 
In the greater depths, more water is held over from irri- 
gation to irrigation, and consequently the changes due 
to varying moisture content do not go on to the same 
degree. It is interesting to note that, in a soil properly 
irrigated, the lower layers of soil to the depth of 10 to 12 
feet are kept, from irrigation to irrigation, within 1 to 4 
per cent of the point at which the structure of the soil 
is the most desirable. 

It is a common observation that irrigation tends to 



70 IRRIGATION PRACTICE 

pack the top soil, and that cultivation must be performed 
after each irrigation, if the top soil is to be kept in a thor- 
oughly loose condition. This is probably due, chiefly, to 
the excessive wetting after each irrigation, which breaks 
down the soil crumbs into a single-grain structure. The 
effect of the successive thorough wetting and drying 
characteristic of irrigation is of interest to the farmer. 

47. Successive wetting and drying. — When irriga- 
tion water is applied, the soil mass expands, only to con- 
tract gradually as the water is lost by evaporation or 
transpiration. The effect of this successive expansion and 
contraction was also investigated by Cameron and 
Gallagher, with rather definite results. At the first irri- 
gation the soil expands, and then contracts to a certain 
definite degree; at the second irrigation the soil does not 
expand quite so much, but contracts a little more than at 
the first irrigation; at the third irrigation the expansion 
is yet smaller and the contraction proportionally larger; 
at each successive irrigation, the soil becomes more and 
more compacted, until a condition of natural packing is 
reached at which the expansion and the contraction, 
after each irrigation, are so nearly the same as to result 
in no practical volume change. If too much or too little 
water is applied at each irrigation, so that the soil is per- 
manently kept too dry or too wet, the condition of natural 
packing is prevented. 

48. Natural packing of soil. — The condition of natural 
packing is, however, far from being the closest possible 
packing; it is rather the packing of highest advantage 
to plant-growth. If the soil has become too tightly 
packed, then the expansions and contractions of succes- 
sive irrigations will tend to loosen the soil, until the con- 
dition of natural packing is reached; if the soil has become 



SOIL CHANGES DUE TO IRRIGATION 71 

too loose, it will be brought to the condition of natural 
packing by excessive irrigations. A soil properly irrigated, 
that is, one which contains, after each irrigation, the 
optimum percentage of water (approximately with the 
field water capacity saturated) will, in time, under this 
law of natural packing by successive irrigations, acquire 
a structure best fitted, considering the nature of the soil, 
for the support of plant-life. The top soil, only, which is 
over-saturated at each irrigation, and thoroughly dried 
out at each cultivation, needs mechanical means to be 
kept in the best structural condition. 

When the soil is in the condition of natural packing, 
the soil-water film is continuous, and water can move 
through it rather freely from soil crumb to soil crumb. 
From the surface of such a soil, if allowed to remain 
uncultivated, the water stored in the lower depths may 
readily escape by evaporation from the top. Under irri- 
gated conditions, where water economy is paramount, 
the top soil must be kept much looser than in the con- 
dition of natural packing. For that reason, as was 
emphasized in the preceding chapter, it is necessary to 
follow every irrigation with a thorough cultivation, so 
that the top soil may always be a dry, loose mulch to 
prevent evaporation. 

49. Soil temperature. — The temperature of the soil 
is often of very high importance, especially in the spring 
at the time of germination and early growth. It is of 
importance, also, at all ages of plant-growth. Patten 
has made elaborate investigations to determine the 
quantity of water that will permit the most ready trans- 
mission of heat in the soil. He found that a medium 
quantity of water, not far removed from that which 
corresponds to the point of easy penetration and largest 



72 IRRIGATION PRACTICE 

volume — the point of optimum water content as dis- 
cussed — is the point at which heat moves most readily 
through the soil. The growing season in the irrigated 
region is usually very warm, and it might be of considera- 
ble importance in hastening maturity, or in aiding plant- 
growth, to enable the soil to absorb much heat and to 
conduct it readily into the lower layers, where the plant 
roots are working. 

This is of special importance in districts where the 
irrigation water is taken from the cold mountain streams 
that are often only a few degrees above the freezing point. 
Under such conditions, the ready absorption and con- 
duction of heat by the soil may determine the rate of 
growth and length of the growing season, both of which 
are often of vital importance. All in all, our knowledge 
of the relation of water to the physical properties of soils 
would indicate that the wise irrigation farmer will apply 
to the soil only moderate quantities of water. Too little 
or too much water at a time are equally dangerous, and 
threaten loss to the farmer. 

50. Water a universal solvent. — Practically every 
known substance is soluble to some degree in pure water. 
The rocks and minerals, the fragments of which consti- 
tute soil are, therefore, partly dissolved in the soil water. 
Many of the common minerals of chief occurence in soils, 
such as apatite, clay, mica, hornblend and serpentine, 
dissolve in water to the amount of 4 per cent to 1 per 
cent of their total weight. The solvent power of water 
depends on a number of conditions, the most important 
of which under field conditions are (1) temperature, (2) 
dissolved carbon dioxide, (3) dissolved inorganic salts, (4) 
dissolved organic compounds, and (5) living organisms. 

The higher the temperature, the more rapidly does 



SOIL CHANGES DUE TO IRRIGATION 73 

solution go on. In districts where irrigation is indispen- 
sable, the average temperature during the growing season 
is generally high, and the solution of soil in the applied 
water goes on rapidly. In many places the irrigation 
water itself, taken from comparatively large rivers, is 
very warm, which, added to the high average daily tem- 
perature, accelerates greatly the rate of solution. In 
other places, however, the water, as it issues from the 
mountain canyons, is almost immediately spread over the 
soil. Such water, fresh from the melting snow-banks, is 
of low temperature and chills the soil considerably, and 
in all probability retards the rate of solution of the soils. 

In practically all natural waters there is an abundance 
of the gas carbon dioxid obtained by the water from 
decaying organic remains in the soils through which it 
passes. Such carbonated waters exert a strongly solvent 
action upon the minerals of the soil ; indeed, carbon dioxid 
is by far the most important of the factors that influence 
the solubility of the soil in water. Natural waters gen- 
erally contain also a large proportion of inorganic salts 
which, as a rule, increase the solvent action of water. 
Likewise, solutions of the organic substances formed from 
the decomposition of plant and animal residues exert a 
strongly solvent effect on soils. Finally, the presence of 
living organisms in irrigation water or in soil have much 
to do with the rate at which the soil constituents are 
dissolved. 

51. Humid and arid soils contrasted. — The solvent 
power of water modifies so deeply the composition and 
properties of soil that it is one of the most important 
factors in the establishment of a rational system of irri- 
gation practice. The soil-making forces, from the begin- 
ning, have tended to make soils more soluble, that is, to 



74 IRRIGATION PRACTICE 

make their constitutents more easily available to plants. 
Under humid conditions, with a high annual rainfall, 
the soluble soil constituents thus formed have been 
largely washed out of the soil into the country drainage 
and finally into the ocean. In arid districts, with a 
scanty rainfall and less ample drainage, most of the soluble 
soil constituents remain in the soil. Humid soils, there- 
fore, contain little soluble matter; arid soils, relatively 
much. This is one of the chief differences between the 
two classes of soils. Normal arid soils do not, however, 
contain large proportions of soluble matter. In an investi- 
gation of a great variety of fertile Utah soils, 50 grams of 
soil were shaken with 500 cc. of distilled water for twenty- 
four hours. The soluble matter thus extracted varied 
from .2 per cent to .48 per cent. Under more abnormal 
conditions, as will be explained in the chapter on alkali, 
soluble matter may be present to the extent of several 
per cent, and then the soil must be subjected to special 
treatment before it can serve the farmer. 

52. Continuous solubility of soils. — It is practically 
impossible to wash the soil so thoroughly as to remove 
from it all substances capable of going into solution. 
Many experiments have been made on this subject, all 
with fairly concordant results. For example, Schultze 
treated a given weight of soil with a definite quantity of 
water for six days, after which the solution was filtered 
off and analyzed. This was repeated every six days dur- 
ing six periods. During the first treatment, 1,000,000 parts 
of solution contained 535 parts of mineral matter dis- 
solved from the soil; during the second, 120; then 261, 203, 
260, and 200 parts during the sixth period. That is, 
while the first treatment dissolved most, every successive 
treatment dissolved considerable quantities of soil con- 



SOIL CHANGES DUE TO IRRIGATION 



75 



constituents, and more went into solution during the 
sixth than during the second period. In all probability, 
if these successive washings had been continued, they 
would have resulted in the continuous removal of appre- 
ciable quantities of valuable soil constituents. The con- 
tinuous solubility of soils has a very important bearing 
upon the permanent production of crops on any one soil. 




Fig 17 Midsummer snow in the tops of the mountains. The source of irrigation 
water. This water is very pure. 



76 IRRIGATION PRACTICE 

King found that eleven successive extractions of soil with 
water removed more than eleven times the quantity of 
some constituents that was extracted the first time. The 
continuous solubility of soils is well established, and it has, 
no doubt, an important bearing on the permanent pro- 
duction of crops. 

Whenever, therefore, irrigation water is applied to 
the soil, a part of the soil is dissolved, providing that the 
substances dissolved by the previous irrigation have been 
somewhat thoroughly removed by plant roots or by 
drainage. Naturally, not all soil constituents are extracted 
at the same rate by successive applications of water. 
Approximately the same quantity of potash goes into 
solution from extraction to extraction, while a very large 
part of the nitrates is extracted during the first applica- 
tion of water, leaving little for the later ones; unless, 
indeed, during the interval between irrigations, nitrates 
have been added or cultural treatments have permitted 
a very rapid rate of nitrification. 

53. Absorption by soils. — The solution of soil con- 
stituents occurs most readily at the surfaces of the soil 
grains. The dissolved substances, under the influence 
of somewhat obscure manifestations of the laws of attrac- 
tion, are held in high concentration very near the sur- 
faces, and the outward movement through the water- 
film of the dissolved materials is very slow. This property 
of firmly holding certain soluble substances near the sur- 
faces of the soil particles, known as absorption, is of tremen- 
dous importance in conserving the fertility of agricultural 
soils, whether under humid or arid conditions. The first 
water added to a soil, as has already been explained, is 
held as thin films around the soil grains. Drainage through 
the soil occurs only after these films have acquired a cer- 



SOIL CHANGES DUE TO IRRIGATION 



77 



tain definite thickness. Water added beyond this point 
fills the capillary tubes and under the influence of gravity 
moves downward into the country drainage. As this 
gravitational water moves downward, the soil-water film 
clinging closely around the soil grains is not materially 
affected. A small part of the outer film may be carried 
downward, but the inner part, near the surfaces of the 
soil grains, where the dissolved soil constituents are held 
in greatest concentration, probably does not move at all 
with the gravitational water. Enough is carried along, 
however, to affect materially the composition of the drain- 
age water. In one of the Utah experiments, water was 
applied to a very loose gravelly soil, scarcely 2 feet deep, 
and underlaid with a cobble rock formation of unknown 
depth. Underground collecting chambers were con- 
structed to collect the drainage water. So gravelly was 
the land that within half an hour after water had been 
applied, it drained through into the lysimeters. As an 
average of one season's test, the following results were 
obtained : 



Parts per million 



Total solids 
Volatile matter 
Lime .. . . . 
Magnesia . . 
Potash . . . 
Phosphoric acid 
Nitric acid . . 




It will be noted from these figures that, even under 
conditions of easy and rapid drainage, much valuable 
material is washed out of the soil. Nevertheless, as will 
be shown, the parts of total solids in 1,000,000 parts of 



78 IRRIGATION PRACTICE 

the drainage water were not much higher than in many of 
the streams and rivers used for irrigation. The lime and 
magnesia were not washed out to any great extent, but 
the potash, phosphoric acid and nitric acid, the three 
most important constituents of the soil, were propor- 
tionally much more abundant in the drainage water than 
in the original irrigation water. Analyses of drainage 
waters in various countries lead to similar results. Hil- 
gard, in a collection of analyses of drainage water from 
European countries, has shown that the parts of total 
solids in 1,000,000 parts of water range from 140 to 721, 
with an average of 352.6, which is somewhat higher than 
the 242 found in the above Utah experiment. 

54. Composition of drainage water. — It may be said 
safely that the concentration of drainage water under 
normal conditions is not extraordinarily high, but hovers 
in the neighborhood of 200 to 400 parts of total solids 
in 1,000,000 parts of water. Under abnormal conditions, 
these figures may be much larger. If, for instance, the 
soil is rich in organic matter, as after heavy manuring, 
the drainage water may show a high proportion of organic 
matter; if the soil is of an alkali nature, the drainage 
water frequently contains tremendously large quantities 
of soluble matter. In one of the reclamation experiments 
of the United States Bureau of Soils at Billings, Mon- 
tana, the drainage water from an alkali tract, which had 
been underdrained for the purpose of removing the alkali, 
contained from 250 to 9,000 parts of dissolved matter in 
1,000,000 parts of water; in the drainage water from a 
similar tract located near Salt Lake City, were found 
10,710 to 20,346 parts of dissolved matter in 1,000,000 
parts of water. These are extraordinary concentrations 
of drainage water which occur only when the soils are 



SOIL CHANGES DUE TO IRRIGATION 79 

abnormally rich in soluble constituents. Normal soils, by 
the power of absorption, retain most of the soluble mate- 
rials, so that the concentration of the drainage water is 
kept low, as above given. 

55. Concentration of soil moisture. — Results of strik- 
ing interest are obtained when the possible concentra- 
tions of soil water are calculated. If it be assumed that 
a soil with .1 per cent of soluble matter under ordinary 
laboratory methods contains an average of 20 per cent of 
moisture to a depth of 10 feet, which is the approximate 
condition of an irrigated clay loam immediately after a 
5-inch irrigation, and if all the soluble matter goes into 
solution in the water thus added, the soil solution will have 
a concentration of about 5,000 parts of dissolved matter 
for every 1,000,000 parts of water. This is far in excess of 
the composition of any drainage water from such soils 
under normal field conditions. Moreover, as evapora- 
tion goes on, this concentration must increase consider- 
ably. Arid soils usually contain more than .1 per cent of 
soluble matter; if .5 per cent is held by the soil, for instance, 
the concentration under the above assumptions will be 
25,000 parts of dissolved substance for every 1,000,000 
parts of water — a concentration larger than that of the 
drainage water from the above mentioned alkali reclama- 
tion tract near Salt Lake City. Little is known, as yet, 
about the exact concentration of soluble matter in the 
film held about the soil grains; but it must be compara- 
tively high. In such solutions the feeding roots of plants 
are bathed. 

56. Loss by drainage. — The repeated application of 
water to soils, in quantities sufficient to drain through, 
results disastrously, because, even though the quantity of 
soluble matter taken out each time is small, in the end the 



80 IRRIGATION PRACTICE 

total is considerable. The evidence of this is found in the 
lean and washed-out soils of humid districts, where the 
rainfall is large enough to permit steady drainage with- 
out the counterbalancing effects of a tropical warmth. 
In arid districts, likewise, where over-irrigation has pre- 
vailed, soils have been permanently injured by the loss 
of plant-food — carried off in the drainage. 

The loss of plant-food is only one of the many injurious 
effects of the excessive use of water. In arid districts the 
drainage water, resulting from over-irrigation, frequently 
accumulates in some lower-lying closed basin, such as in 
the lowest part of a valley. At this point the ground 
water rises higher and higher as excessive irrigation is 
practised on the higher land, until the water-table is so 
near the surface that water may be lifted from it to the 
surface by capillary attraction. When this condition has 
been reached, continuous evaporation from the soil sur- 
face occurs. The soluble matters contained by the water 
which is left behind increase, first, the concentration of 
the ground water, and secondly, as evaporation goes on, 
fill the upper layers of soil with soluble salts, often with 
a formation of an alkali crust. Over-irrigation thus 
becomes one of the chief sources of the dreaded alkali. 

The disastrous results of the excessive use of water 
prevail over large areas in almost every irrigated section 
of the world. Leaky canals have permitted large quanti- 
ties of water to soak through great areas of fertile soils, 
until, heavily charged with precious plant-food, they have 
accumulated in lower basins. Farmers, anxious to pro- 
tect themselves against the drought, and believing that 
the more water used the more certain would be the crop, 
have so over-irrigated their lands as to permit a more or 
less constant drainage into subsoil and lower-lying places. 



SOIL CHANGES DUE TO IRRIGATION 81 

In view of this danger, the irrigation farmer must so con- 
trol the application of water to the soil that no more is 
added than is necessary to produce the maximum film 
around the soil grains. Drainage must, as a rule, be 
avoided. A knowledge of the depth and character of the 
soil and devices for measuring water make this easily done. 

57. Upward leaching. — In yet another manner is the 
nature of the soil materially influenced by irrigation. If 
water is applied in moderation, and according to the best 
principles of irrigation, the soil-water film is simply thick- 
ened to a distance greater or smaller, according to the 
quantity applied. The water thus added is in part lost 
by evaporation at the top soil, and in part is taken from 
the soil through the plant roots. While the plant roots 
often penetrate the soil to a depth of 8 to 10 feet or more, 
yet the greatest abundance of plant roots is found in the 
upper soil. Under heavy irrigation, especially, when 
plants are not obliged to drive their roots deeply in search 
of water, the greatest root-development is usually found 
in the upper 3 feet or so of the soil. However, even these 
surface roots draw water from much greater depths; for, 
as has already been explained, the removal of water in an 
upper soil results in a slow capillary flow of water from 
below, to re-establish equilibrium. As the water moves 
upward, to replace that removed by the roots, it carries 
with it some of the materials dissolved from the lower 
soil layers. 

Under wise irrigation, therefore, there is a gradual 
movement of the soluble soil constituents toward the sur- 
face, where the soil moisture often becomes so concen- 
trated that the salts crystallize out and form layers of 
alkali. When irrigation is again applied, these soluble 
matters are in part washed downward; but, owing to the 

F 



82 IRRIGATION PRACTICE 

laws of absorption, they are held very near to the surfaces 
of the soil grains and are not easily dislodged by the 
gravitational water passing through the first foot. The 
downward movement of water is comparatively rapid and 
largely gravitational; the upward movement compara- 
tively slow and capillary. Therefore, in irrigated soils, 
fairly rich in soluble matters, the tendency is to concen- 
trate the soluble materials in or near the top soil. 

Arid soils are frequently 50 to 70 feet deep and at times 
that distance from the ground water. The irrigation 
water in such soils, if wisely applied, moves downward 10 
to 15 feet. It is only, then, within this limit that the 
soluble matters are moved upward. If the soil is rich in 
soluble matters, this concentration may result in injury 
to the plants; if, as is the usual case, the percentage of 
soluble matters is low, no injury results, but the plant- 
foods from lower depths are made easily available to 
plants. Even where the soil is rich in soluble materials, 
the farmer can, by judicious irrigation, and by the proper 
cultivation of the soil, keep the soluble substances so 
well distributed that no damage can result to the growing 
crop. 

58. Salinity of river waters. — The natural waters 
used in irrigation are never quite pure, for no natural 
water is free from dissolved substances. Even rain-water 
dissolves from the air considerable quantities of nitrates 
and other substances. When the water that falls upon the 
land as rain or snow moves toward the rivers by seeping 
through the soil or by flowing over the ground, it succeeds 
in dissolving, during its descent, relatively large quanti- 
ties of soil materials. The more deeply such water soaks 
into the soil before it finally reappears as a spring, or the 
longer it flows over the soil, the higher will be its concen- 



SOIL CHANGES DUE TO IRRIGATION 



83 



tration of dissolved substances. This is well shown by 
any of the analyses made of river water taken at different 
distances from the river head. For instance, in the fol- 
lowing rivers the salinity or the parts of soluble matter in 
1,000,000 parts of water was as follows: 



River 


Near the 
head 


Lower 
down 


Cache la Poudre 




37 

148 

185 

892 

6,670 


1,011 


Arkansas .... 




21,034 


Bear 


637 


Jordan, Utah 


1,090 


Chalis, Algeria 


1,182 



The Chalis River, Algeria, is an exception to the rule 
because tributaries, carrying relatively pure water, enter 
and dilute the main river near its lower end. 

The quantity of dissolved substances in natural water, 
that is, the salinity, varies from exceedingly small quan- 
tities, as in rain-water, to almost saturated solutions, as in 
the waters of the Dead Sea and the Great Salt Lake. The 
following table, based upon the classical work on "The 
Data of Geochemistry," by F. W. Clarke, shows the pro- 
portions of dissolved substances found in some of the 
river waters of the world. No such table, however elabo- 
rately constructed, can be wholly accurate. At best, only 
a few of the rivers of the world have been subjected to 
chemical analysis, and even the rivers that have been 
most thoroughly studied, have not been analysed at all 
seasons of the year for a sufficient number of years to 
make the averages absolute in their values. 



84 



IRRIGATION PRACTICE 



Dissolved Substances in River Waters 
(Parts per million) 



Locality 


Range 


Remarks 


Min. 


Max. 


United States — 








Atlantic Slope .... 


15 


140 


Nearly all under 100 


Mississippi Basin . . . 


90 


2,323 


One-half under 300 


Southwestern rivers . . 


321 


2,384 


Three-fourths above 700 


Northwestern rivers . . 


31 


1,481 


Nearly all under 100 


Great Basin (no outlet) 


185 


1,090 






119 


2,412 


Nearly half under 200 


Canada — 








St. Lawrence Basin. . . 


1 


298 




Saskatchewan Basin . . 


115 


551 




Europe — 










31 


286 






134 


254 






49 


447 






126 


299 




Elbe 


13 


221 




South America — 






37 


59 






40 


9,185 




Nile 


130 

86 


174 
122 









It will be observed that, in the United States, the 
waters of highest average purity, that is, of lowest con- 
centration, are those on the Atlantic Coast; those of the 
Mississippi Basin and of the great Northwest come next; 
the waters of the southwestern rivers, including the 
Colorado, are still higher in their average content of solu- 
ble matter; while those of the California rivers stand 
between those of the Mississippi River and those of the 
Southwest. The rivers of the Great Basin, which, after a 
short journey from the mountain headwaters, reach the 
interior lake into which their load is deposited, are less 
concentrated than the rivers of the Southwest and more 
like those of the Mississippi River Basin. 



SOIL CHANGES DUE TO IRRIGATION 85 

The concentration of river waters, at least in the 
United States, appears to vary with the rainfall. In 
humid districts, where the soils are more thoroughly 
water-washed, and where the run-off is large, the quantity 
of dissolved material is small. In arid districts, with 
soils richer in soluble matter, the concentration of the 
river waters increases. While the annual rainfall is not 
the only factor determining the concentration of river 
waters, yet it determines, in large measure, the quantity 
of soluble substances. The same general law may be 
observed in the data dealing with the Canadian rivers. 
In the St. Lawrence Basin, the proportion of dissolved 
substances in the river waters is considerably smaller 
than in the Saskatchewan Basin, which is more of a semi- 
arid character. Similarly, the data from the river waters 
of Europe shows a variation with the general climatic 
conditions, especially with the rainfall. 

The Nile, famous in irrigation history, does not carry 
a great abundance of soluble material. It stands in this 
respect between the waters of the Mississippi and those 
of the Great Basin. The data of the above table, which 
are representative of the rivers of the world, show that 
the quantity of dissolved substances in river waters is 
not extraordinarily large. In most cases, the waters of 
even long rivers in arid districts are less concentrated than 
the ordinary drainage water of agricultural fields. 

The river waters of humid regions, with low total con- 
centration, are comparatively rich in carbonates; those 
of arid regions, on the other hand, with high concentra- 
tion, contain more sulfates and chlorides than carbon- 
ates. This is explained when it is recalled that, under 
humid conditions, the native vegetation grows abundantly 
and the proportion of soil humus is much larger than 



86 IRRIGATION PRACTICE 

under more arid conditions. Water passing through such 
humid soils naturally takes up from the humus much 
carbon dioxide. 

59. Salinity of lake waters. — The waters of the great 
lakes of the world, from which irrigation waters are 
frequently taken, vary as largely as do the river waters. 
The water of mountain lakes that are fed directly by 
the melting snows contains little dissolved matter. For 
example, the water of Lake Tahoe, in Nevada, contains 
only 73 parts of dissolved substances to 1,000,000 parts 
of water; whereas, the water of Sevier Lake, in Utah, con- 
tains 86,400 parts, and, in the water of the Great Salt 
Lake there are nearly 300,000 parts of dissolved sub- 
stances. Ocean water, as another example, contains 
about 39,000 parts of dissolved substances in 1,000,000 
parts of water. Naturally the lakes that contain the 
most concentrated solutions are in almost every instance 
those of interior basins with no outlet to the ocean. The 
water runs into these basins and as it is gradually evap- 
orated it leaves behind its load of soluble materials to 
concentrate the remaining water. In the course of time, 
such waters become saturated with certain substances 
which then crystallize out. This is the case with the Great 
Salt Lake and many other well-known interior lakes of 
western United States and other arid parts of the world. 

60. Salinity of mineral springs. — The most heavily 
charged waters, however, save those of interior basin 
lakes, issue as mineral springs in many parts of the world. 
The high degree of salinity of such waters seems to be 
due, as already suggested, to the fact that the percolated 
water has passed over subterranean layers of soluble 
material which is brought up in solution when the spring 
issues from the soil. The salinity of such waters varies 



SOIL CHANGES DUE TO IRRIGATION 87 

from extreme purity to a concentration comparable with 
saturated waters of inland lakes. 

61. Soil moisture and natural waters compared. — As 
shown above, the soil solution of a clayey loam contain- 
ing about .1 per cent of soluble matter will contain in the 
neighborhood of 5,000 parts of dissolved matter for 1,000,- 
000 parts of water. This is considerably higher than the 
concentration of the larger number of river waters, or even 
of mineral springs. In the arid regions, the soluble matter 
of soils often exceeds .1 per cent, and the concentration 
of the soil solution, after irrigation, is probably higher 
than 5,000. Moreover, if the top soil is not thoroughly 
stirred, evaporation from the soil surface goes on very 
rapidly and the soil solution becomes so concentrated 
that, before the next irrigation, the concentration must be 
nearly twice what it is immediately after an irrigation. 
The effect of varying quantities of dissolved substances 
in irrigation water on the growth of plants will be dis- 
cussed in the chapter on alkali. It is of very great impor- 
tance to the irrigation farmer. 

62. Ash constituents added by irrigation water. — 
When the quantities of water used in irrigation are so 
large that there is a constant drainage through the soil, 
the only probable effect of the water on the soil is the wash- 
ing out of certain soil constitutents. When water is 
added in moderation, so that the soil is filled to a certain 
depth, but not in sufficient quantity to drain through, the 
soluble matters contained by the water must of necessity 
remain in the soil, except as they may be utilized by the 
plant. Under existing practices 2 acre-feet of water 
represent a very moderate annual irrigation. On suffi- 
ciently deep soils, if the single applications are not too 
large, this quantity of water does not cause material 



88 IRRIGATION PRACTICE 

drainage. It is then possible to calculate the probable 
quantities of soluble salts deposited in the soil to a depth 
of 10 to 15 feet during one season's irrigation. In the 
arid regions, 250 parts of dissolved substances in 1,000,000 
parts of water are accounted unusually low, unless obnox- 
ious substances are admixed. Such a water, applied to the 
soil to a depth of 2 feet throughout the season, allowing 
for no drainage, would leave in an acre of soil throughout 
the season, approximately 1,300 pounds of solid matter. 
This repeated, year after year, would naturally run into 
large amounts, although some would, undoubtedly, be 
taken up by the plants in their growth and used for the 
elaboration of plant tissues. 

At the Utah Station, a large number of analyses were 
made of crops grown under irrigation, and it was found 
that in wheat kernels the ash content was about 2.5 per 
cent and, in wheat straw, about 10 per cent. A thirty- 
bushel wheat crop would then abstract from the soil 
about 345 pounds of mineral matter, or a little more than 
one-fourth of the total quantity added by irrigation. 
Lucern contained about 8.5 per cent of ash materials, in 
which case a crop of 10,000 pounds would contain approx- 
imately 850 pounds, or a little more than two-thirds of 
the materials left by the irrigation water. None of the 
crops ordinarily grown under irrigation takes up the 
quantity of soluble substances added to the soil by 2 
acre-feet of water, providing drainage is prevented. It 
must be remembered, in this connection, that irrigation 
waters do not always contain all the essential plant-foods, 
or in the right proportion. While a water may add to 
the soil more solid matter than the crop needs, the indi- 
vidual constituents may be wholly or in part absent, and 
must be supplied by the soil. 



SOIL CHANGES DUE TO IRRIGATION 89 

Under more modern and improved methods of irriga- 
tion, first-class crops are frequently raised with 1 or 1J^ 
acre-feet of water. In such cases, the crop more nearly 
takes up the substances added to the soil by irrigation 
water. On the other hand, the water used for irrigation 
ordinarily contains more than 250 parts of dissolved sub- 
stances in 1,000,000 parts of water. If the salinity is 500, 
2 acre-feet of water would add to one acre, 2,600 pounds 
of solid substances, and waters richer in mineral matters 
would leave in the soil tremendous quantities of solid 
matters. It is readily seen, therefore, how profoundly 
irrigation water may affect soils under irrigation. Should 
the irrigation water be heavily charged with substances 
deleterious to soil or crop, immediate and irreparable 
damage may be done. Little definite information con- 
cerning the whole subject is as yet available. It is quite 
evident, however, that the methods of irrigation must be 
varied with regard to the composition of the water used. 

63. Use of concentrated waters. — An irrigation water 
of medium concentration may be used safely in modera- 
tion, although it should be so used as to leave as little as 
possible of its constituents in the soil. When concentrated 
waters are used, excessive quantities are applied to force 
drainage, so that the concentration of the free water in 
the soil after irrigation is never above that of the water 
used. This is the good reason behind the practice of 
farmers, in districts where the soils or waters are heavy 
in alkali, to use more water throughout the season than 
in districts where the soils are freer from alkali and the 
water of low concentration. This principle is frequently 
the essential one in building up a district which of neces- 
ity must depend upon highly mineralized water for its 
supply of irrigation water. 



90 IRRIGATION PRACTICE 

64. Need of water surveys. — The substances con- 
tained by the water may in themselves be harmless ; but, 
since they are applied to the soil from year to year in 
such large quantities, they undoubtedly often fill many of 
the capillary soil spaces or are deposited on the surfaces 
of the soil grains, and thus affect the chemical composi- 
tion and the granular condition of the soil. This subject 
has as yet been poorly investigated, but is worthy of 
careful investigation, so that irrigation practices may be 
rationalized from the point of view of the varying com- 
position of irrigation water. Systematic chemical sur- 
veys of irrigation waters should be made in connection 
with the study of the soils to which the waters are to be 
applied. Only when such data are abundantly at hand 
will it be possible to formulate for each section irrigation 
practices that will be permanently satisfactory. In the 
present stage of irrigation progress, it has become very 
important to know the composition of irrigation waters. 
As irrigation becomes older more problems will arise, 
many of which can be solved only by a more thorough 
knowledge of the waters used on irrigated soils. Water 
surveys are as legitimate in irrigated districts as are soil 
surveys. 

65. Composition of natural waters. — While the total 
quantity of soluble matter found in a given volume of 
irrigation water is of great importance, the composition 
of such soluble matter is of equal importance. In soils 
are found the great majority of the chemical elements 
and particularly those that are essential in plant-growth. 
In the following table may be found the composition of a 
number of natural waters selected from the data given 
by Clarke. 



SOIL CHANGES DUE TO IRRIGATION 



91 





X 

3 


(D , 


_ » to p or 


3°0 

DO 




?3 0$ £•£ 2. jvHkS 




bonic 
uric £ 
ne) . 
ric ac 
um) 
nesiui 
im) . 
ium) 
3 (0 
inum 
oa) . 








w *. 


E- s: 


O p 






5- 




*—• 


£2. 








CD 








W S 








O 




















>->> 




















HH 




















►1 




















O 




















3 




















P 




















P 




















a 
















1— ' tO H- ' 


CO 


1. — River waters 


J—N3 M Oi CO O O Oi In! 

OS <I h- 1 •<! l£. CO CO O h- 1 
<J Cn M(Dh(DO00*> 


Cn 

— 1 

Cn 


Average for world. 
— F. W. Clarke 


h-> i— > to 4^- 

• o c >*>• w CO- to W h 


2. — Rio Grande 

at 
Messilla, N. M. 


. CO MOOi^. Cn --J Cn 
CO -g tO tO CO CO CO rf^ 


i— ' t— > I— > i— > to 

• • po oi co p • vi w p 


3. — Snake River 

at 
Blackfoot, Idaho 


. . h-> co bs to . O CO CO 

O 00 4*- O i-» C5 t- 1 


t— ' I— 1 M H H 

Cm Mpij^pOO^OO 


4. — San Joaquin 

River at 
Lathrop, Calif. 


com oboool-'biorf^rfi. 

0000 00H-'tOCOrf».tOt-'CO 


CO Ox 

H O W M' Ox -4 O 

. . J- 1 Cn <l to . *£>. Ci to 


5. — Ocean water. 
Challenger 


HtDWO 00 to f 


expedition 


CO Ox 




• • co to j- 1 p • pi p • 


6. — Great Salt 


H O tO M , 1— ' OS . 


Lake water 


CO ^J Cl ^J i— > Ci 




CO OS 




O • •— ' h- 1 rf^ • •— > © • 


7.— Chloride 


. © . ox bx bo . bb, 


water 


Ox M to Cn rf*. -^ 




I— ' I— ' •<! 




p • p j-> to p • to to • 


8. — Sulphate 


© . to to ■<! bx . as bx . 


water 


Ox to CO CD CO to © 




to Ox 




to CO C j-» CO p • to © Cn 


9. — Carbonate 


rf^C75 -<l CO •-* to . ►£■ Cn CO 


water 


tOtO COtOCnQO tOh^tO 




i-» co to 




top pcopipip'pi^ito 


10. — Nitrate 


Cn h- O Cn t— ' b O '^ QC br 


water 




00 


to 


a 


cc 


-sj CO ?o 


Cn 


-q 


00 





a 

o 

O 
3 CO 

M 

d H 

3 o 

CD 

13 O 

c+- W 
03 J 

2.JZJ 

3 E 

I ^ 

H 
S3 
CO 



92 IRRIGATION PRACTICE 

The first column shows the average composition (rarer 
elements being excluded) of river waters for the world. 
All the elements necessary for plant-growth are present. 
The carbonic acid, combined chiefly with calcium, is in 
largest abundance. Sulfuric acid, in combination with 
calcium, magnesium, sodium and possibly potassium, is 
also present in large abundance. Chlorine is third in 
abundance. Even nitric acid, vitally important for plant- 
growth, is present in small quantities. In the three fol- 
lowing columns are analyses of the waters of three great 
rivers of western America, used largely for irrigation pur- 
poses. All the necessary plant-foods are present, but in 
very different proportions, which, undoubtedly, will 
affect, differently, the conditions of plant-growth. In 
column 5 is the average composition of ocean waters as 
determined by the Challenger expedition. It differs 
materially from the analysis in column 1 which is a world 
average for river water. The carbonic acid has practically 
disappeared, no doubt precipitated by the lime, and the 
sodium and chlorine have increased tremendously. In 
column 6 is an analysis of the water of the Great Salt 
Lake, which is a body of water practically saturated with 
common salt. It resembles ocean water, but carbonic 
acid is totally absent; the proportion of calcium and 
magnesium lower; of potassium higher. 

66. Classification of natural waters. — Considering 
the composition of the soluble materials held by natural 
waters, especially those used in irrigation, they may be 
classified as follows: Those rich in chloride of sodium are 
called chloride waters; those rich in sulfates, especially 
of sodium and calcium, are sulfate waters; those rich in 
carbonates, especially of sodium, are carbonate waters; 
those rich in borates are borate waters; those rich in free 



SOIL CHANGES DUE TO IRRIGATION 93 

acids, are acid waters. This classification may be extended 
to cover any water as soon as its predominating con- 
stituent is known. The above are the leading classes. A 
typical analysis of a water in several of the above classes 
will be found in the last four columns of the preceding 
table. 

This classification of natural waters is very useful in 
irrigation practice, and especially important in consider- 
ing the alkali question. For the purposes of this chapter 
it is sufficient to make clear that practically all known 
natural waters, unless rain-water and water coming 
immediately from the melted snow be excepted, contain 
varying quantities of all the essential elements of plant- 
growth. Moreover, the variations in the proportions of 
the constituents of water are so great that while the waters 
may be roughly classified as chloride, sulfate or car- 
bonate waters, there is a host of intermediate kinds which 
overlap two or more groups. For an exact understanding 
of the chemical behavior of an irrigation water on the 
soil or crop, an analysis of the water in question must 
be available. 

67. Plant-food value of irrigation water. — The infor- 
mation found in the preceding table makes possible some 
interesting calculations. The quantity of plant nutrients, 
such as nitrogen, potassium, phosphorus and lime removed 
from an acre of soil by some of the common crops, has been 
computed by Warington. His results, obtained under 
humid conditions, do not differ greatly from those that 
might be obtained under irrigated conditions, and, until 
data from irrigated crops are obtained, may be used with 
approximate accuracy. A crop of wheat yielding thirty 
bushels to the acre requires at least about thirty pounds of 
potash, ten pounds of lime, twenty pounds of phosphoric 



94 IRRIGATION PRACTICE 

acid and forty-eight pounds of nitrogen. By using the 
smallest percentage, 22 per cent of potash, in the above 
table, 2 acre-feet of water would yield a little less than six 
pounds of potash, a quantity entirely insufficient for the 
production of a crop. By using the averages of some of the 
other waters in the table, the potash added by 2 acre- 
feet is ample to supply the crop needs. Any of the waters 
in the table, save No. 6, with only 17 per cent lime, would 
supply amply the needs of the crop for lime. In most 
waters, the nitric acid is present in natural waters in very 
small quantities, but it is not likely that the quantity 
of water ordinarily used in irrigation throughout a season 
would be sufficient to supply the crop needs. Phosphoric 
acid is also present in small quantities and seldom can 
supply, thoroughly, the crop needs. While, therefore, the 
total soluble material contained by ordinary water 
appears to be quite sufficient in quantity to supply the 
total needs of the plant, the specific substances required 
for successful plant-growth are fully met only in a few 
waters. With moderate irrigations and waters of aver- 
age composition, plants must draw upon the soil for at 
least some of the constituents needed in their growth — 
notably for phosphoric acid, nitrogen and potash. Waters 
in which these substances are present in larger propor- 
tions may supply all the needs of the crop for mineral 
matters. 

The property of the soil to retain certain ingredients 
of the water that may be passing through it is of impor- 
tance in this connection. Lime, magnesia, potash (notably 
in clay soils), chlorine, and practically all the ingredients 
of irrigation water, are partly absorbed by the soil through 
which the water passes. The substances that are absorbed 
and the degree of absorption are determined by the com- 



SOIL CHANGES DUE TO IRRIGATION 



95 



position of the soil and of the water. To establish equilib- 
rium between the soil and the water, in conformity with 
chemical and physical laws, substances dissolved in the 
irrigation water are absorbed and held by the soil, or 
corresponding substances are taken from the soil to 
enrich the drainage water. Because of this soil power of 
absorption, the water that drains from the soil is propor- 




Fig. 18. Badly corroded ditch due to excessive fall. On a larger scale this is the 

action of swift rivers. 



tionally of a much different composition from the water 
which was originally added to the soil. This is brought 
out by the analysis on page 77. 

68. Suspended matter in river waters. — By far the 
larger part of river waters carry not only large quan- 
tities of dissolved substances; they carry, also, considera- 
ble loads of suspended solid matter. This suspended 
material is naturally derived from the washing effect of 



96 



IRRIGATION PRACTICE 



the snow-water, rain-water and floods, chiefly among the 
highlands, near the headwaters of the river course. Note 
the following table : 

Suspended Matter in River Waters 

(Parts per million) 



River 



Belle Fourche, at Belle Fourche, S. D 
Bighorn, at Fort Custer, Mont. . . 

Colorado, at Yuma, Ariz 

Red, at Mangun, Okla 

Gunnison, at Whitewater, Colo. . . 

Pecos, at Carlsbad, N. M 

Pecos, at Dayton, N. M 

Rio Grande, at El Paso, Texas . . . 

Salt, at Roosevelt, Ariz 

North Platte, at Laramie, Wyo. . . 



Minimum 


Maximum 


56 


7,120 


18 


2,860 


741 


30,800 





16,800 


32 


4,090 





1,480 


44 


11,400 


8 


83,900 


40 


6,940 


62 


3,450 



The quantity of suspended matter as shown in the 
above table is very variable and frequently very large. 
Rivers rising in well-forested districts, or those that 
travel only a short distance before they empty into the 
lake or main river, are often comparatively free from sus- 
pended matter. The Colorado and the Rio Grande Rivers 
carry more suspended matter than any other of the great 
rivers of the United States. As shown above, as high as 
84,000 parts of suspended matter in 1,000,000 parts of 
water — nearly 8.5 per cent — have been found in the water 
of the Rio Grande at El Paso, Texas. The Colorado at 
Yuma, Arizona, has carried nearly 31,000 parts, or more 
than 3 per cent, of suspended matter in 1,000,000 parts of 
water. When the immense volumes of water in such rivers 
are considered, it is readily understood that quantities of 
suspended matter almost beyond human comprehension, 
are carried from the highlands tributary to the river, 



SOIL CHANGES DUE TO IRRIGATION 



97 




Fig. 19. Walled ditch to prevent erosion of easily "washed" 
soil. 

during each season's flow. Large rivers, all over the world, 
carry similar loads of suspended matter. Famous exam- 
ples are the Nile, the Danube, the Rhine and many other 

G 



98 IRRIGATION PRACTICE 

historical rivers, a large number of which are partially 
diverted for irrigation purposes. (Figs. 18, 19.) 

69. Seasonal variation of suspended matter. — The 
suspended matter carried by a river varies in quantity 
from month to month. This is well shown in the follow- 
ing table, constructed from the records of the Green 
River, at Jensen, Utah, during the years 1905 and 1906. 

Suspended Matter Carried by the Green River, at Jensen, 
Utah, Each Month During the Year 1905-06. 

(In parts per million) 

April 2,278 October 666 

May 917 November 79 

June 415 December 64 

July 91 January 17 

August 613 February 28 

September 4,749 March 3,170 

In March and April, during the time of the heavy 
spring rains, the loads of sediment were very large; as 
also in September and October, when the fall rains 
occurred. During the summer months of June, July and 
August, when only occasional showers fell, the suspended 
matter was low; and in November, December, January 
and February, when the ground was largely covered with 
snow, it was even smaller. 

During the seasons of the year when the lands around 
the headwaters of the rivers are not covered with snow 
and ice, the quantity of suspended matter carried by a 
river varies directly with the time and quantity of pre- 
cipitation. A sudden flood will render the river turbid 
with suspended matter, and the longer seasonal floods of 
spring and fall are characterized by long periods of muddy 
water. In a part of the western United States where the 
growing season is rainless, the water is clearer during the 



t4O0O 


*/an. 


reJb. 


Mar. 


/7/>r. 


Mot/ 


June 


*Su/y 


/Tt/f 


Sept 


Oe/-. 


/for. 


Dec. 


fZOOO 




















































toooo 




















































eooo 




















































eooo 
































Jl 


















4000 






■ 
























1* 


















eooo 






1 


1 
























A 


















o 




»^I1 ^ ^ 

















Fia. 20. Daily discharge of Malheur River (second-feet). 



/+000 



/2000 



toooo 



COOO 



eooo 



40OO\ 



eooo. 




Fig. 21. Daily discharge of Mackenzie River (second-feet). 

(99) 



100 IRRIGATION PRACTICE 

irrigation season than either just before or after. In other 
parts, where summer rains prevail, the irrigation water 
is often heavily loaded with suspended matter. (Figs. 
20, 21.) 

70. Suspended matter added to soil by irrigation. — 
Considerable quantities of sediment may be added to the 
soil during a season's irrigation. If 2 acre-feet of water 
are used annually for the production of crops, a calcula- 
tion may be made similar to that which was made con- 
cerning the soluble matter added to the soil. During the 
time of summer floods, few waters contain less than 1,000 
parts of suspended matter in 1,000,000 parts of water. If 
this were continued throughout the season, it would 
mean an addition to each acre of land of over 5,000 
pounds of sediment. The southwestern rivers, which 
carry, ordinarily, throughout the season much more sedi- 
ment than this, add to each acre during each irrigating 
season an extremely large total quantity. It has been 
reported from Arizona that, frequently, the sediment 
of one season's irrigations covers the land to a thickness 
of 4 to 6 inches. In rivers with less sediment, these 
effects are not so visible, but wherever irrigation is prac- 
tised, especially in arid districts, a large quantity of solid 
matter is deposited on and in the soil. This, continued 
year after year, will certainly affect the productive power 
of the soil. 

71. Suspended matters derived from surface soils. — 
The suspended matters in river waters come chiefly from 
the surface washings of the lands near the headquarters of 
the rivers. The character of the suspended matters car- 
ried by rivers varies, therefore, with the surface nature 
of the soils from which the sediments are derived. If the 
contributing soils are sandy, the suspended matter will 



SOIL CHANGES DUE TO IRRIGATION 101 

be sandy; if the soils are loamy or clayey, the sediments 
will be correspondingly more rich in clayey materials. 
Usually, however, only the silty or finer particles reach 
the lower portions of the river where the irrigation canals 
are taken out. The coarser or more sandy particles are 
deposited in the first quiet places of the river and do not, 
ordinarily, reach the lower lands, except, perhaps, in 
times of high water, when even the sand deposits of earlier 
years may be torn up and whirled down to the irrigated 
districts. 

The top or surface soil is always most vigorously 
affected by sunshine, air, water and biological agencies; 
therefore the top soil is the most fertile part of the soil. 
It is this fertile soil layer that is washed into the rivers, 
finally perhaps to be deposited on the farmers' fields. 
Eventually, then, the farmer covers his own land with the 
fertile surface soil of the mountain slopes and upland 
valleys. 

72. Composition of river sediments. — River sediments 
have been analysed in the United States, in Europe and 
in Egypt. The results show that river muds are somewhat 
richer in the essential plant-foods than the ordinary 
fertile soils which the water serves. It has been estimated 
by Forbes that the market value of the fertilizing con- 
stituents in three samples of Salt River mud, to the acre- 
foot of water, varied from $7.98 to $25.51. These figures 
should be given respectful consideration by the farmer 
who does not content himself with using one acre-foot 
of water. When the fertilizing value of these sediments 
is considered in connection with the fertilizing value of 
the dissolved materials, one of the great advantages of 
irrigation is made evident. Under many of the rivers of 
the irrigated section, proper methods of irrigation should 



102 



IRRIGATION PRACTICE 



make the draft of the plant upon the soil so small as to 
extend greatly the productive power of the soil. 

73. Physical effects of sediments. — The physical 
effects of the addition of river silts to the soil are not, 
however, always uniformly beneficial. On a sandy soil, 
the river silts usually bind the soil together and make it 
more firm, of better water-holding power and of easier 




Fig. 22. Deposit in field of suspended matter from irrigation water. 

cultivation. On a heavy clay, if the river sediment is of 
a loamy character, the clay is mellowed and lightened 
and, therefore, improved. However, if the silt is very 
fine or of a clayey nature, its application to a clay soil 
or even to a loam soil might be disadvantageous, because 
of the finer texture that it would produce. Herein lies 
the danger in using irrigation water that carries consider- 
able quantities of suspended matter. River mud is usually 



SOIL CHANGES DUE TO IRRIGATION 103 

of a very fine texture. When dry, it crusts and forms a 
hard covering, which does not readily admit water or air 
into the soil. This necessarily interferes seriously with 
plant-growth. One season's irrigation is not greatly 
injurious, but if repeated year after year, unless proper 
cultural treatments are employed it may result disas- 
trously. 

Another danger, of less importance, resulting from the 
use of water containing much suspended matter, is that 
occasionally the finely suspended matter clings closely 
around the roots of the plant, and, as it dries and con- 
tracts, injures the plant mechanically; or it may produce 
a type of sun-scald, not yet clearly understood. It is 
not wise to apply to young plants during a period of 
high temperature an abundance of water heavily charged 
with suspended matter. (Fig. 22.) 

74. Cultural treatment of sediments. — It is not, 
however, a very difficult problem to meet and overcome 
this condition. The annual silt deposit should be plowed 
into the soil thoroughly each fall or spring, and, to keep 
the top soil open, thorough cultivation should be prac- 
tised throughout the growing season. It has been observed 
that fields of wheat, irrigated with water rich in mud, 
have produced unusually large crops wherever the sedi- 
ment was plowed in from year to year, and the soil thor- 
oughly disked or harrowed in the spring after the high- 
water irrigation, with its load of silt, had been applied. 
The young wheat is not injured materially by such early 
harrowing, and the advantages resulting from the breaking 
of the silt crust are shown in unusually large crops. On 
the other hand, an alfalfa field, cultivated in the old- 
fashioned way, that is, which receives no cultural help 
throughout the season, is soon made to suffer severely 



104 IRRIGATION PRACTICE 

by the accumulation of the annual silt deposits, which 
effectually shut out air from the soil and make it almost 
impossible for water to penetrate into the lower soil 
layers. If this one danger be avoided, the suspended 
matter in irrigation waters may be made a source of wealth 
to the irrigation farmer. 

75. Effect of sediments on crop yields. — Forbes has 
made some interesting experiments on the effects of the 
river silt on the production of crops in Arizona. Similar, 
but not so carefully made, observations have been made 
in other sections of the world. The general conclusion 
seems to be that wherever water, carrying sediments, is 
applied without attention being given the silt deposits, 
the crop-yields tend to decrease. Whenever, however, 
the physical disadvantages discussed above are offset by 
proper tillage, great financial advantages result from the 
fertile matter carried by the irrigation waters. In fact, 
the fertile suspended matters, carried at the irrigation 
season, should increase materially the value of water- 
rights from such sources. The tremendous value of the 
overflow of the Nile, heavy with suspended matter brought 
from the African highlands, is a familiar historical fact. 
In India, South Africa, Europe and the United States, 
there are districts in which the lands have higher values 
because of the quantities of sediment carried by the 
irrigation streams. 

The irrigation farmer deals with a much more compli- 
cated problem than does his brother who depends simply 
upon the natural precipitation for the moisture supply. 
To the irrigation farmer the soil is one factor, the rainfall 
another, and the water that he uses may be almost as 
important a factor as the soil itself. 

76. Water and soil life. — Soil moisture also exerts a 



SOIL CHANGES DUE TO IRRIGATION 105 

distinct effect on the living organisms in the soil. The 
detailed relations that exist between soil life and varying 
soil moisture are yet to be determined, and will furnish 
another and most important chapter in irrigation practice. 
Very few investigations have been made on this phase of 
irrigation, although the field is full of promise. 

It is well known that bacteria and other formsof low 
life flourish best when in the presence of an abundance of 
water, and the statement is commonly made that the 
greatest effects of bacterial life are obtained when an 
excess of water is available. While these findings are 
generally true, it must be observed that few studies of 
bacterial activity have been made under an environment 
similar to that which prevails in the soil. Low forms of 
life, like higher ones, require various foods in addition to 
water; and these substances must be in solution at a 
certain concentration. Under irrigation, as already shown, 
the concentration of the soil solution may be varied con- 
siderably. When over-irrigation is practised, the soil 
solution is kept very dilute; when no irrigation is prac- 
tised, during rainless summers, it may be kept very con- 
centrated. This phase of the subject, in relation to soil 
life, is yet to be studied. 

Stewart and Greaves have studied, at the Utah Sta- 
tion, the effect of varying applications of water on the 
nitrifying organisms. Series of field plats were grown to 
different crops. Each series received irrigation from 25 
inches to none. The soil was ideally adapted to rapid 
bacterial action. The work was continued over eight 
years, so that the conclusions may be accepted with con- 
siderable assurance of their truth. It was found that 
the nitric nitrogen content never exceeded 300 pounds to 
a depth of 10 feet. The application of irrigation water 



106 IRRIGATION PRACTICE 

had a distinctly beneficial effect upon the formation of 
nitric nitrogen. The greatest total production was 
observed when 15 inches of water were applied. The 
greatest production to the inch of water was found, how- 
ever, when the minimum quantity of water was used. The 
use of the maximum quantity of water, 25 inches, decreased 
the total yield, and gave the smallest yield of nitrates per 
inch of water used. A medium quantity of water appeared 
best, therefore, for the activity of the nitrifying organisms. 

In the same investigations, it was found that the con- 
centration of the soil solution, in nitrates, was always 
greater as more irrigation water was used. 

In view of the tremendously great importance of soil 
life in the maintenance of soil fertility, it should be care- 
fully studied under the conditions of irrigation. 

REFERENCES 

Cameron, F. K. The Soil Solution. Chemical Publishing Company, 

Easton, Pa. (1911). 
Cameron, F. K., and Gallagher, F. E. Moisture Content and 

Physical Condition of Soils. United States Department of 

Agriculture, Bureau of Soils, Bulletin No. 50 (1908). 
Cameron, F. K., and Bell, James M. The Mineral Constituents 

of the Soil Solution. United States Department of Agriculture, 

Bureau of Soils, Bulletin No. 30 (1905). 
Clarke, F. W. The Data of Geochemistry. Second edition. United 

States Geological Survey, Bulletin No. 491 (1911). 
Collins, W. D. The Quality of the Surface Waters of Illinois. 

United States Geological Survey, Water Supply Paper No. 

239 (1910). 
Cushman, A. S. The Effect of Water on Rock Powders. United 

States Department of Agriculture, Bureau of Chemistry, 

Bulletin No. 92 (1905). 
Dole, R. B. Analyses of Waters East of the 100th Meridian. 

United States Geological Survey, Water Supply Paper No. 236 

(1909). 



SOIL CHANGES DUE TO IRRIGATION 107 

Forbes, R. H. The River Irrigating Waters of Arizona. Arizona 

Experiment Station, Bulletin No. 44 (1902). 
Forbes, R. H. Irrigating Sediments and Their Effects Upon Crops. 

Arizona Experiment Station, Bulletin No. 53 (1906). 
Hare, R. F., and Mitchell, S. R. Composition of Some New- 
Mexico Waters. New Mexico Experiment Station, Bulletin 

No. 83 (1912). 
Hilgard, E. W. Soils. Chapters VII and XVIII (pp. 327-333). 

The Macmillan Company (1906). 
King, F. H. Investigations in Soil Management. United States 

Department of Agriculture, Bureau of Soils, Bulletin No. 25 

(1905). 
King, F. H. Investigations in Soil Management. Madison, Wis. 

(1904). 
Patten, H. E. Heat Transference in Soils. United States Depart- 
ment of Agriculture, Bureau of Soils, Bulletin No. 59 (1909). 
Stabler, Herman. Some Stream Waters of the Western United 

States. United States Geological Survey, Water Supply Paper 

No. 274 (1911). 
Stewart, Robert, and Greaves, J. E. Study of the Production 

and Movement of Nitric Nitrogen in an Irrigated Soil. Utah 

Experiment Station, Bulletin No. 106 (1909). 
Stewart, Robert, and Greaves, J. E. Production and Movement 
of Nitric Nitrogen in Soil. Centralblatt fur Bakteriologie, 
Band 34, p. 115 (1912). 
Widtsoe, J. A., and Stewart, Robert. The Dry-Farm Soils of 

Utah. Utah Experiment Station, Bulletin No. 122 (1913). 
Winkle, W. Van, and Eaton, F. M. The Quality of the Surface 

Waters of California. United States Geological Survey, Water 

Supply Paper No. 237 (1910). 



CHAPTER VI 

CONDITIONS DETERMINING THE USE OF SOIL 
MOISTURE BY PLANTS 

The discussion in the preceding chapters has taken 
no account of the effect on plants of soil moisture. Yet, 
the plant is a most important factor, for it uses immense 
quantities of water throughout the season, and the rate 
of use is very difficult to control. It becomes necessary, 
therefore, to investigate the relationship of the plant to 
the water added to the soil in irrigation. The relation- 
ship is of particular importance, because, under irriga- 
tion, the farmer may apply different quantities of water, 
at stated times, throughout the growing season. That is, 
under irrigation a soil-moisture control is possible, which 
is not possessed by any other system of agriculture. 

The essential question in agriculture is always, "To 
what extent can the farmer control the conditions of 
plant-production?" Where water is the critical factor, 
as in irrigation, it is of first importance to know how the 
absorption of water from the soil by plants may be con- 
trolled. Once this is known, systems of farming may be 
planned whereby the scanty water supply may be made to 
reclaim the largest possible area of land, or to produce 
the largest yield of high-quality crops. 

This chapter is devoted to a discussion of the condi- 
tions that determine the rate at which water is taken 
from the soil by plants. The rate at which water is used is 
ordinarily different from the total quantity used by the 

(108) 



USE OF SOIL MOISTURE BY PLANTS 109 

plant throughout the season. A rapidly growing plant, 
for example, may use daily a very large quantity of water 
but only for a relatively short time, while a more slowly 
growing plant, using daily a smal er quantity of water, 
but for a longer period of time, may in the end use much 
more water. The rate at which a plant uses water refers 
invariably to the quantity used per hour, day or any other 
unit of time, during certain periods of its growth, and is 
not invariably a measure of the total water-needs of the 
crop. 

77. Absorption of water by roots. — The roots are the 
organs of water-absorption. Practically no water is taken 
into the plants by the stems or leaves even under con- 
ditions of heavy rainfall. In the absorption of water 
from the soil, the young roots are most active, and, of 
these, only certain parts are actively engaged in water- 
absorption. At the tips of the young roots are numerous 
fine hairs, known as root-hairs, clustering near the tip of 
the root. These are the organs of the plant that absorb 
soil water. As the root-hairs grow older, they lose their 
power of water-absorption; in fact, they are active only 
when they are in actual process of growth. Water-absorp- 
tion, therefore, occurs near the tips of the growing roots, 
and, whenever the plant ceases to grow, water-absorption 
also ceases. 

The root-hairs are filled with a solution of various 
substances, as yet poorly understood, which play an 
important part in the absorption from the soil of water 
and plant-food. Owing to their minuteness, the root- 
hairs are in most cases immersed in the moisture film that 
surrounds the soil particles, and the soil moisture is taken 
directly into the roots from this film by the process of 
osmosis. Without entering into a discussion of the com- 



110 IRRIGATION PRACTICE 

plicated movement of water from the soil into the plant, 
it may be said that the concentration of the solution in 
the root-hairs is higher than that of the soil-water solu- 
tion. The water tends, therefore, to move from the soil 
into the roots to make the solutions inside and outside 
of the roots of the same concentration. If it should 
occur that the solutions inside and outside the root-hairs 
were of the same concentration, that is to say, if they 
contained the same substances in the same proportional 
amounts, there would be no further inward movement of 
water. Moreover, if the soil moisture should become 
stronger than the water within the root-hairs, water 
would tend to pass from the plant into the soil. This is 
the condition that prevails in the alkali lands of the 
West, and is often the cause of the death of plants grow- 
ing on such lands. 

78. Transpiration. — There is a constant movement of 
water, holding in solution the indispensable plant nutri- 
ents, after it has entered the root-hairs, through the roots, 
stems and into the leaves. At the leaf surfaces evapora- 
tion occurs, and, there, much of the water taken from the 
soil passes into the air as invisible water vapor. The 
rapidity of this current is often considerable. Ordinarily 
it varies from 1 to 6 feet an hour, although observations 
on record show that the movement often reaches the rate 
of 18 feet an hour. In an actively growing plant it does 
not then take long for the water in the soil to find its way 
to the uppermost parts of the plant and to be evaporated 
from the leaf surfaces. This movement of water from the 
soil, through the plant, into the air, is the process known 
as transpiration. If the current of water passing through 
the plant is stopped for any considerable length of time, 
the plant is injured and death often results. Transpira- 



USE OF SOIL MOISTURE BY PLANTS 



111 



tion appears to be a process wholly necessary to plant life. 
Our question is, To what extent may it be reduced with- 
out injuring plant-growth? 

79. The initial percentage of soil moisture. — The 
most important factor in determining the rate of loss of 
soil water is the average percentage of water found in 
the soil at the beginning, known as the initial percentage. 
All other conditions being the same, the loss of water 
from two plants during a definite period of time varies 
as the initial percentage. The following table, selected 
from a great number of experiments on this subject 
made at the Utah Station, illustrates the law: 



Length of period 


Average per cent 
of water at 
beginning 


Pounds of water 

lost per 

square foot 


Ten days 


21.84 
13.18 


25.05 


Ten days 


10.51 








8.66 


14.54 



The soil which contained at the beginning of the 
experiment 21.84 per cent of water, lost during ten days 
more than twenty-five pounds of water to the square foot; 
whereas the soil that contained 13.18 per cent of water at 
the beginning of the period lost only about ten and one- 
half pounds of water to the square foot. It seems very 
clear that the rate of loss of water from a soil increases as 
the initial percentage of water in the soil increases; that 
is, the higher the initial percentage of water, the greater 
the loss; the lower the initial percentage, the smaller the 
loss. 

The reason for this effect of the initial percentage can 
be fairly well understood. The fine root-hairs come into 



112 IRRIGATION PRACTICE 

contact with a comparatively small area of the soil-water 
film. As water is drawn into the plant, there must be a 
flow of water toward the point of contact between the 
active roots and the soil-moisture film. If the film is 
thick, the water will move with some freedom and the 
plant, in a given time and with the expenditure of a given 
amount of energy, will absorb a larger quantity of water 
than would be possible if the film were thin and offered 
greater resistance to the moving water. The same prin- 
ciple has been shown to hold generally, as when water 
evaporates directly from the surface of the soil. The per- 
centage of water in the soil is a fair measure of the thick- 
ness of the soil-water film, and the rate of loss of water 
from the soil increases, therefore, as the initial percentage 
of moisture in the soil increases. This is the same as saying 
that the more water contained by the soil to a given depth, 
the more is lost in a given time by plant- and sun-action. 
This important law seems to imply that plants are not 
able to regulate the quantity of water taken up by roots; 
but rather that, assuming all other factors to be uniform, 
the rate of transpiration varies only with the ease with 
which water may be obtained. If this be true, plants 
may easily waste water if too much is found in the zone 
of root-growth; unless, indeed, the rate of growth is 
proportional to the use of water — a condition which does 
not exist. Here is evidently, then, because of the inability 
of the plant to regulate its consumption of soil moisture, a 
danger which the farmer must carefully heed. While the 
plant cannot possibly be prevented from taking more 
water from moist than from dry soils, yet, the farmer 
may so reduce the percentage of soil moisture that the 
plant is not always absorbing water at its maximum 
capacity. Manifestly, in spite of all that can be done. 



USE OF SOIL MOISTURE BY PLANTS 113 

immediately after an irrigation, when the soil is moist, 
the plant will of necessity use much more moisture per 
unit of time than later when the soil is not so moist. 

A question of importance in this connection is this: 
If two fields contain respectively 20 per cent and 10 per 
cent of water, will the loss of soil moisture during any 
definite period be twice as great from the one field as 
from the other? From the data in our possession, it 
may be answered that the losses are proportionally 
larger from the wettest soils. This may be seen from the 
table on page 111. The difference in the moisture per 
cent is only 8.66 but the difference in the pounds of 
water lost to the square foot during the same period was 
14.54. That is to say, the wetter the soil became, the 
more rapid did the proportional loss of moisture become. 
This important phase of the law of the initial percentage 
might have been foretold by recalling that the thinner the 
soil-moisture film, the more firmly is it held by the soil. 
Under the point of lento-capillarity, plants can absorb the 
soil moisture only with the greatest difficulty; above this 
point, the absorption goes on much more rapidly. Pre- 
liminary experiments seem to show that, if the lento-cap- 
illary water of a soil be subtracted from the percentage 
of water held by each of two or more soils, and the cube 
roots be taken of the remainders, that is, of the water in 
true capillary condition, an approximately correct meas- 
ure of the relative ease with which plants can abstract 
water from the soil is obtained. 

The law of the initial percentage teaches the impor- 
tant doctrine that moderate irrigations are in all proba- 
bility more economical than heavy ones; and it may 
explain why heavy irrigations, as will be shown later, do 
not yield proportional increases of dry matter, 

H 



114 



IRRIGATION PRACTICE 



80. Distribution of water in the soil. — The distribu- 
tion of water in the soil is likewise important in determi- 
ning the rate at which plants use water. 



Length of period 


Per cent 

of water in 

first foot 


Average per cent 

of water to 

depth of 8 feet 


Pounds of water 

lost per 

square foot 


Ten days .... 
Ten days .... 


23.68 
17.25 


17.69 
16.85 


18.24 
13.55 


Difference . . . 


6.43 


0.84 


4.69 



As shown in the above table, two soils may each con- 
tain approximately an average of 17 per cent of water to 
a depth of 8 feet, but in the first the percentage of mois- 
ture in the first foot is over 23 per cent, while in the second 
the percentage of moisture in the first foot is about 17 
per cent. That is, the distribution of water is not the 
same in the two soils. In such a case, more water is lost 
from the soil in which the water is heaped up near the 
surface. The more evenly the water is distributed to 
the full depth of root-action, the more slowly does the 
plant consume the water during any given period of time. 
The data in the table show that during a period of ten 
days, where the top soil was wettest, 4.69 pounds more 
were lost to the square foot than where the water was 
more evenly distributed throughout the soil. 

The greater water loss from soils, otherwise alike, that 
contain a large proportion of water in the first foot, may 
be explained in part by the greater root-development in 
the upper layers of the soil. Roots are well developed in 
arid soils to a depth of 10 or more feet, but the larger part 
of the small roots are developed within the upper 3 or 4 
feet. Moreover, when the top soil is abundantly rich in 



USE OF SOIL MOISTURE BY PLANTS 115 

water, direct evaporation from the soil occurs much more 
freely. 

To prevent the accumulation of water in the upper 
foot, and the consequently greater loss of soil moisture, 
the land should be plowed deeply, so that the irrigation 
water may move easily and rapidly to the lower soil 
layers. For the same reason, the soil should be kept 
moist enough to permit water to descend quickly. The 
limiting of root-development in the upper foot by deep 
cultivation may also be advantageous. Whatever device 
the farmer may employ to distribute water uniformly to 
comparatively great depths, and to prevent the excessive 
development of roots in the upper soil layers, will tend to 
reduce the rate at which plants will absorb water from 
the soil. Under the law of distribution, as explained in 
Chapter III, the proportion of water is normally greater 
in the upper than in the lower soil layers; yet, by proper 
cultural treatments, it is possible to effect the most com- 
plete distribution in the shortest time, and thus to con- 
serve the water. 

81. The effect of time. — Closely connected with the 
law of the initial percentage, and derived from it, is the 
further law that as time goes on, the rate of loss of soil 
moisture becomes smaller and smaller. In the beginning, 
when the soil is moist, much water is lost. After the first 
day, there is a smaller quantity of water in the soil, and 
the rate of loss will be a trifle smaller, and so on, day after 
day, until a period is reached which finds the soil so dry 
that the plant can no longer draw water from it. On a 
shallow soil, during two weeks after irrigation, more than 
31 per cent, or nearly one-third, of the total loss of water 
occurred during the first three days after irrigation; 29 
per cent the next four days; 23 per cent the next three 



116 IRRIGATION PRACTICE 

days; and 17 per cent the last four days of the two-week 
period. Similar proportional figures were found for 
longer periods. On a deep soil, of good water-holding 
power, during fourteen days after irrigation, 62 per cent 
of the total loss occurred during the first seven days, and 
only 38 per cent during the second week. Such figures, 
which might be multiplied by drawing from many experi- 
ments on the subject, show that methods designed to 
conserve soil moisture should be put into operation as 
soon as possible after irrigation. Especially to prevent 
direct evaporation, the soil should be cultivated as soon 
as possible after irrigation — in fact, as soon as the soil is 
dry enough to support the cultivator without injuring the 
structure of the soil. 

82. The depth of soil. — The deeper the soil, the aver- 
age percentage of soil moisture being the same, the larger 
is the loss of water in a given period of time. This law is 
easily understood. If two soils weighing 100 pounds to 
the cubic foot are 1 and 2 feet deep respectively, and both 
contain an average of 20 per cent of moisture, they will 
contain respectively to the square foot of surface, and to 
their full depth, twenty and forty pounds of water. Dur- 
ing the first day, each soil will lose, say, two pounds of 
water. There will remain, at the beginning of the second 
day, in the shallow soil, eighteen pounds, and in the deep 
soil, thirty-eight pounds of water, or 18 per cent and 19 
per cent — the deeper soil having a higher percentage of 
moisture. During the second day, then, in accordance with 
the law of the initial percentage, the deeper soil will lose 
more water than will the shallow soil. The difference 
will become more marked with each passing day. Other 
factors enter in, as the fuller development of plant roots 
in deep soil, but, assuming all other factors to be the same, 



USE OF SOIL MOISTURE BY PLANTS 117 

the deeper the soil the more rapidly will the soil lose its 
moisture. It does not follow from this law that the deep 
soil will dry out more rapidly than a shallow one. On the 
contrary, since, in the case above suggested, there is only 
half as much water in the shallow soil as in the deep soil, 
the shallow soil, with a smaller rate of loss, will dry out 
very much more quickly than will the deep soil with a 
larger rate of loss. This must be understood and remem- 
bered by the farmer who is dealing with shallow soils. 

Various kinds of shallow soils occur in the irrigated 
district. In some cases a hardpan has been formed a few 
feet below the surface, which does not readily disintegrate 
under the influence of irrigation. This leaves a compara- 
tively shallow soil in which to store moisture, which dries 
out quickly and must be irrigated frequently. Many soils 
are underlaid at a depth of a few feet with coarse, loose 
gravel, through which water percolates and is lost. Such 
shallow soils must be treated as are soils with hardpan 
near the surface. However, where an impervious hardpan 
underlays the soil, if too much water be applied, there is 
greater danger of water-logging; whereas, on soils under- 
laid with loose gravel there is little such danger, for the 
excess moisture percolates downward and is lost. From 
another point of view, also, this is important. On shallow 
soils of any kind, a given quantity of water cannot dis- 
tribute itself over considerable depths. As a consequence, 
the percentage of soil moisture is higher, which causes a 
more rapid loss of soil moisture. From the point of view 
of the conservation of soil moisture, such soils are, there- 
fore, less economical than deep ones. 

83. Physical composition of soils. — The rate of loss 
of soil moisture from cropped fields varies with the physical 
composition of the soil. In a fine soil, a given quantity of 



118 IRRIGATION PRACTICE 

water will be spread over a much larger surface of soil 
particles and the film, therefore, will be thinner; hence, the 
water will be absorbed at a slower rate than from a coarse- 
grained soil, which exposes a smaller surface and over 
which the same quantity of water forms a much thicker 
film. It may be demonstrated that, with a given quantity 
of water, the thickness of the film that forms over soil 
particles varies as the radius of the soil grains. That is, 
if in a given soil the particles are twice as large in diame- 
ter as in another, a given quantity of water added to 
these soils will form a film twice as thick in the coarse 
soil as in the fine one. Consequently, plants growing on 
fine-grained soils will use water at a lower rate than 
those growing on coarse-grained soils. In other words, 
under conditions otherwise uniform, the more clay a 
soil contains the less rapidly does the plant draw water 
from it. 

84. Chemical composition of soils. — The chemical 
composition of the soil also determines the rate at which 
plants take moisture from the soil. This factor is of 
especial importance because it is within the power of the 
farmer to change, at least in a small way, the chemical 
composition of the soil, by proper methods of tillage, or by 
the direct addition to the soil of manure or commercial 
fertilizers. As explained in Chapter V, the chemical sub- 
stances of which the soil is composed are gradually dis- 
solved by the soil moisture. The soil solution of different 
soils varies, therefore, with the composition of the soil 
and the quantity of water added. The root-hairs, through 
which soil moisture is absorbed, lie immersed in the soil 
solution. The rate at which water is taken from the soil 
by these plant roots depends largely upon the relative 
strength of the solution inside and outside of the root- 



USE OF SOIL MOISTURE BY PLANTS 119 

hairs. In general, the stronger the soil solution the less 
rapidly will plants take water from the soil with a given 
rate of growth. This is not an invariable law, however, 
since it depends, in part, on the nature of the soil materials 
that go into solution. If the soil solution is acid, the rate 
of absorption by plants is accelerated; if alkaline, it is 
retarded. In the vast majority of cases, soils are alkaline 
rather than acid. Especially in arid regions is the occur- 
rence of acid soils infrequent. 

The soil solutions of fertile soils are usually more con- 
centrated than those of less fertile soils. It follows, there- 
fore that, the more fertile a soil is, the less rapidly does the 
plant absorb the soil moisture with a given rate of growth. 
This law, which has been demonstrated in a number of 
interesting experiments, teaches the farmer the great 
importance of keeping the soil in a most fertile condition. 
Bouyoucos has made some interesting observations on 
this subject. As above stated, the more concentrated the 
soil solution is, the less rapidly do plants take moisture 
from the soil. Yet this concentration need not always be 
due to plant-food, for Bouyoucos has shown that an 
innocuous soluble substance, such as common salt or 
sodium sulfate, if added to the soil, decreases the rate 
at which the plants take water from the soil. This is 
important because of the fact that in a great many 
irrigated soils of the country, resulting from the peculiar 
climatic conditions, are found considerable quantities of 
common salt, and soluble salts of magnesium, calcium 
and other elements which are not needed as plant-foods. 
These accumulations, ordinarily known as alkali, when 
present in large quantities, are a serious menace to suc- 
cessful agriculture. The above law seems to show, how- 
ever, that the presence of such materials in the soil may 



120 IRRIGATION PRACTICE 

be of distinct value in diminishing the rate of loss of 
water from the soil. Consequently it follows, also, that 
on alkali soils the rate at which water is transpired is 
smaller than on soils that are free from alkali. This 
may, in a small measure, account for the fact that even 
cropped alkali lands remain rather moist throughout the 
season. 

If all this be true, however, it is within the power of 
the farmer so to maintain the soluble material in the 
soil as to permit the plant to draw water from the soil 
at the slowest possible rate. By proper methods of 
cultivation whereby plant-food is set free, by the appli- 
cation of commercial fertilizers, of manure, or by innocu- 
ous salts, such as the abundant sodium sulfate, it is 
possible to maintain the soil solution in a high degree of 
concentration and thereby secure for the plant the neces- 
sary foods at a very slow rate. This fundamentally impor- 
tant factor in the economical use of water by plants, has 
received in the past practically no attention, but is now 
becoming more generally recognized. 

85. Plowing. — Among the cultural processes that have 
for their purpose the reduction of the rate of loss of water 
from the soil, none is more important than the ancient 
art of plowing, which is the fundamental practice in all 
agriculture. From the point of view of the irrigation 
farmer, and the saving of soil moisture, plowing has dis- 
tinct advantages. First, it permits the easier descent of 
water into the soil and consequently a more rapid and more 
uniform distribution throughout the soil. This results 
in a smaller rate of loss.. Second, thorough and careful 
plowing at the right time of the year, preferably in the 
fall, gives every soil activity new freedom, thereby releas- 
ing more plant-food and rendering the soil solution more 



USE OF SOIL MOISTURE BY PLANTS 121 

concentrated. Thorough and careful plowing results in a 
diminished rate of loss of water from cropped soils. 

86. Cultivation. — The frequent cultivation of the soil, 
as discussed in Chapter III, has for its purpose the reduc- 
tion of the direct evaporation of water from the soil. 
It has, however, a number of other beneficial effects of 
high importance to the irrigation farmer. For example, 
cultivation diminishes the rate at which plants take water 
from the soil, and further, as will be shown later, it even 
diminishes the quantity of water required to produce a 
given quantity of dry matter. Cultivation is essential 
in irrigation agriculture because it diminishes the direct 
evaporation from the soil and because it reduces the 
quantity of water transpired by plants. It is a practice 
that should be observed faithfully by the farmer through- 
out the season. After every rainfall and after every irri- 
gation, just as far as possible from spring until fall, the 
soil should be carefully stirred by the farmer. The cost 
of such treatment will be more than paid for in the greater 
yields of crops, and in the greater producing power of 
water. 

87. Manuring. — It is quite evident, from what has 
been said already, that manuring, or the adding to the 
soil of plant-foods, under a given rate of growth will tend 
to reduce evaporation. This is another argument in behalf 
of manuring — a practice which, unfortunately, has not 
been carefully observed by the irrigation farmers of 
America. As time goes on and water becomes more 
precious, and the population of the arid region increases, 
the art of manuring, whether with natural or artificial 
fertilizers, will acquire a greater and greater importance. 

88. Vigor of plant. — The rate of loss of soil moisture 
due to plants depends very largely upon the vigor of the 



122 IRRIGATION PRACTICE 

plant itself. A sickly plant evidently does not require, nor 
can it use, so large quantities of water as a strong, healthy 
plant. Many farmers fail to understand this simple and 
almost self-evident law, and therefore apply to a crop 
poorly developed fully as much water as is applied to 
one which is growing vigorously. 

89. Root-system. — Another factor of importance in 
determining the rate of loss of soil water due to plants is 
the development of the root-system. If the roots have 
been developed near the surface, more water will be used 
from the top soil than if the roots have been more evenly 
distributed throughout the soil, and the energy expended 
in lifting the water from the lower depths is increased. 
To drive the roots downward, water should not be applied 
too early in the season, nor should it be applied in such 
quantities as to make it unnecessary for the lower roots 
to continue their work. Only when the roots fill the soil 
to the greatest depth in the most thorough manner, will 
the soil moisture be used most economically. 

90. Age of plants. — The age of a plant naturally 
determines, largely, the rate at which soil moisture is 
absorbed. A plant increases very rapidly in dry weight, 
up to the time of flowering. After this time the increase 
is slight, and finally diminishes. The rate at which plants 
use water varies somewhat in the same way. There is a 
steady increase in the rate at which plants use water 
from early spring up to flowering; after which there is 
a diminution, until, when the plant is old, it uses water 
at a very low rate. A similar relation exists between 
growth and water-use of biennial crops such as sugar 
beets. The effect of the age of plants on the rate of loss 
of soil water is well shown in the following table: 



USE OF SOIL MOISTURE BY PLANTS 



123 



Pounds of Water Lost Daily Per Square Foot 
(Rate increases to flowering, then decreases.) 


Crop 


July 


August 


September 


Corn 


2.06 
1.33 
1.29 


2.46 
1.53 
0.95 


2 07 


Sugar beets 


1.04 


Wheat 









It is to be remembered that, in this table, the initial 
percentages are not in all cases the same, so that the dif- 
ferent crops cannot be compared as to their power to 
abstract water. The only legitimate use of the table is to 
compare the quantities of water for each crop that were 
lost in July, August and September — the months of the 
growing season. In the case of corn, the greatest loss came 
in August; while in July and September, the loss was prac- 
tically the same. In the case of sugar beets, the greatest 
loss also came in August; the next in July, and the smallest 
in September. In the case of wheat, the largest loss came 
in July and the smallest in August. These variations are 
readily explained by remembering that, under the climatic 
conditions prevailing, the wheat matured in July and was 
harvested in August, thus corresponding with the rates 
of loss as shown above; while the corn and sugar beets 
continued their vigorous growth into September. The 
time of most rapid growth is usually the time of greatest 
daily water use. 

91. The kind of crop. — The kind of crop also influences, 
materially, the rate at which water is taken from the soil. 
No two crops appear to be exactly alike in their power to 
absorb soil moisture. Much work is yet to be done on 
this subject before really definite results can be given. 
Meanwhile, some general laws have been observed which 
can safely be stated, at least until further knowledge is 



124 IRRIGATION PRACTICE 

gathered. It appears that crops which mature early use 
water more rapidly than those which have a longer grow- 
ing period. For example, under the conditions prevailing 
in the irrigated sections of the United States, wheat and 
oats use daily more water than corn, beets or potatoes, 
although in the aggregate, wheat and oats use much less 
water than do the longer-growing crops. Wheat, oats 
and similar crops hasten on to maturity and, in so doing, 
use water at a very rapid rate. Corn, potatoes and sugar 
beets continue their steady growth throughout the season, 
and the rate at which they use water is considerably 
smaller. Lucern, which is cut from two to four or even 
more times during the season, behaves pretty much as if 
it were a series of quickly growing crops. 

The rate at which various crops use water may be 
roughly estimated by the degree to which soils are dried 
out during long periods without irrigation by the respec- 
tive crops. Experiments show that, from this point of 
view, lucern comes first, followed, in order, by wheat, 
oats, corn, sugar beets and potatoes. This is practically 
the order obtained in direct experimentation. More 
information is needed regarding the relative powers of 
different crops to abstract soil moisture. 

92. The seasons. — The farmer may, in a measure, 
control most of the factors already discussed, but he is 
helpless when it comes to controlling the varying seasons. 
No one factor is so powerful in influencing crop-growth 
as are the seasons, and with this factor the farmer must 
always reckon. The average temperature throughout 
the season is of first importance in determining plant- 
growth, and therefore, in a large measure, the rate at 
which the plant uses water. With a high average tempera- 
ture, plant-growth is rapid and the daily loss of soil 



USE OF SOIL MOISTURE BY PLANTS 125 

moisture is great. Sunshine is next in importance. The 
more abundant the sunshine throughout the growing 
season, the more favorably affected is plant-growth, and 
the more rapid is the loss of the soil moisture. Third in 
importance is the relative humidity of the air. The drier 
the air, the more rapidly does water evaporate from the 
plant, and, therefore, the more steadily does water move 
through the plant from the soil. Following these three 
factors — temperature, sunshine and humidity — are winds 
and all manner of air movements. These dry out the 
soil and increase the rate at which water passes through 
the plant to supply the more rapid evaporation from the 
plant. Winds are always a serious factor of water-loss, 
largely beyond the control of the farmer. Rains, especially 
slight ones, during the growing season are a menace, for 
they keep the top soil moist and make possible a rapid 
direct evaporation; however, they tend to diminish trans- 
piration, from the reduction in the relative humidity 
which follows them. These factors, fundamental in 
determining the season, determine largely the evaporation 
of water from the soil itself. Experiments have shown that 
the rate of loss of soil moisture due to plant-action is 
frequently varied as a result of the seasons. 

The factors of water-loss discussed in this chapter 
are those of most importance to the irrigation farmer. 
Many of them may be controlled more or less perfectly 
and, therefore, they should be well understood. 

REFERENCES 

Botjyoucos, George J. Transpiration of Wheat Seedlings aa 
Affected by Soils, by Solutions of Different Densities, and by 
Various Chemical Compounds. Proceedings of the American 
Society of Agronomy, Vol. Ill, pp. 130-191 (1911). 



126 IRRIGATION PRACTICE 

Briggs, Lyman J., and Shautz, H. L. The Water Requirements of 
Plants. United States Department of Agriculture, Bureau of 
Plant Industry, Bulletins Nos. 284 and 285 (1913). 

Buergerstein, A. Die Transpiration der Pflanzen (1904). 

Widtsoe, J. A., and McLaughlin, W. W. The Movement of Water 
in Irrigated Soils. Utah Experiment Station, Bulletin No. 115 
(1912). 

Widtsoe, J. A. Factors Influencing Evaporation and Transpira- 
tion. Utah Experiment Station, Bulletin No. 105 (1909). 

Utah Station Staff. Irrigation Investigations. Utah Experiment 
Station, Bulletin No. 80 (1902). 



CHAPTER VII 
THE WATER-COST OF DRY MATTER 

The steady transpiration stream of water, passing from 
the soil through all growing plants to be evaporated at the 
leaves, is responsible for the largest loss of soil moisture. 
This loss is, also, the most difficult to control; for, as 
shown in previous chapters, direct evaporation from the 
soil may be largely prevented by simply stirring the top 
soil, but many complex factors are involved in the loss 
of water by transpiration. Many experiments have been 
made to determine the relative quantities of water lost 
by evaporation and transpiration. While no absolute 
numbers of general application have been obtained, yet, 
when the land is not cultivated to prevent evaporation, 
one and one-half times as much water evaporates ordi- 
narily from the vigorous, growing plant as from the soil. 
When the soil is well tilled, and direct evaporation thus 
reduced, the water lost by transpiration is often five to 
ten times greater than the quantity lost by evaporation 
from the corresponding area of soil. 

This great loss of soil moisture by transpiration is a 
matter of much concern to the farmer, who pursues his 
work in the hope of reaping the largest harvest from 
the land, water and labor employed. Especially, where 
water is scarce or irrigation is practised, the important 
question is whether the increased yield is in proportion 
to the quantity of water passing through the crop by 
transpiration. If the yield increases in proportion to the 

(127) 



128 IRRIGATION PRACTICE 

increase in transpiration, there will be no need to reduce 
transpiration. If, on the other hand, the water-cost of 
the crop is partly independent of the transpiration stream, 
it may become necessary to decrease or increase trans- 
piration to a point at which the largest yield of dry matter 
is produced with the smallest quantity of water. Only 
when this is done does irrigation give its greatest returns. 

93. Carbon assimilation. — Practically one-half of a 
plant consists of the element carbon. From 2 to 10 per 
cent consists of mineral matter, taken from the soil, and 
brought into the plant in the process of transpiration. 
The remainder of the plant consists of the elements of 
water combined with carbon and mineral matter to form 
the variety of plant constituents. 

The carbon, constituting one-half or more of the dry 
plant, is obtained by the plant from the air through leaf- 
action. The gas carbon dioxid constitutes about three 
parts in 10,000 parts of air. As the air washes against 
the leaves of plants, this gas finds its way into the leaves 
of green plants through small openings, known as stomata, 
or breathing pores, which occur in great abundance, 
especially on the lower side of the leaves. The stomata 
are delicately adjusted valves which as they open and close 
are entrances to relatively large open spaces within the 
leaves themselves. When the carbon dioxid enters the 
leaves through the breathing pores, it is rapidly absorbed 
by the juices of the leaves and immediately decomposed 
into the element carbon and the element oxygen. The 
oxygen is returned to the atmosphere, while the carbon 
is retained and combined with water and other substances 
with the formation of sugars, starches and other valuable 
plant constituents. This process of carbon assimilation 
continues without intermission in green plants during the 



THE WATER-COST OF DRY MATTER 129 

time of bright daylight or of sunshine. Chlorophyll, the 
green coloring matter of higher plants, and sunshine are 
indispensable for this wonderful decomposition and new 
composition. 

A simple calculation will show how actively the leaves 
of the plant must be at work decomposing carbon dioxid 
and building up the new compounds derived from the 
assimilated carbon. It is not uncommon in the irrigated 
section that an acre of well-developed lucern yields, in 
one season, 10,000 pounds of dry matter. One-half, or 
5,000 pounds, of this crop consists of the element carbon, 
obtained from the gas carbon dioxid of the air by the 
countless leaves that have swayed back and forth in the 
air throughout the growing season. Each tiny leaf has 
done but a small part of the work, but the total gives a 
lively appreciation of the tremendous activity of plant 
leaves. 

94. Plant age and carbon assimilation. — The rate at 
which this assimilation of carbon, or "growth," takes place 
varies with the maturity of the plant. To illustrate, at 
the Utah Station careful measurements were made of the 
total acre weight of dry matter in a crop of lucern from 
May 4 to August 24, covering practically the whole of 
the growing season. In early May, when the plant was 
well established, the weekly gain of dry matter was 
something over 300 pounds to the acre; this increased 
steadily until just before the time of flowering, when it 
was nearly 800 pounds, after which it gradually decreased 
until late in July, when there was a loss instead of gain. 
This represents a general law of plant-growth. At the 
beginning of the growing season the daily or weekly gains 
of the crop are small, but they increase steadily and rather 
rapidly, providing the conditions of growth are favorable, 
I 



130 IRRIGATION PRACTICE 

until the maximum rate of increase occurs about the time 
of flowering. After flowering, as seed-formation sets in, 
the rate of growth becomes smaller, for, from that time 
on, the main energies of the plant are no longer directed 
to the increase in dry matter, but concern themselves 
more largely with the elaboration of the food materials 
already gathered into seed to be used for the perpetuation 
of the species. 

Evidently, since water is unquestionably necessary in 
plant-growth, the needs of the plant for water probably 
increase about as the rate of growth increases. From ear- 
liest spring the water-need of a plant increases, until it 
reaches a maximum about the time of flowering, after 
which it gradually diminishes. This supposition, as will 
later be shown, is confirmed by actual field experiments. 

95. Conditions of growth. — Many factors influence, 
to some degree, the rate of growth of a crop. Most of 
them are uncontrollable and, therefore, of little impor- 
tance to the farmer. Those that concern him most, 
especially under arid conditions are (1) heat, (2) light, (3) 
oxygen, (4) mineral food and (5) moisture supply. With 
given vitality and inherent qualities, these factors will 
act vigorously upon the assimilation of carbon. If the 
temperature is too low, the life activities of the plant 
become slower and may finally cease. The higher the 
temperature, within a rather large range, the more rapidly 
does growth go on. Light, especially sunlight, is another 
powerful factor in furthering the assimilation of carbon. 
Oxygen is a prime factor in plant-growth, for without it 
the processes of oxidation, corresponding to breathing in 
the higher animals, cannot proceed; and, without this 
function, plant life cannot long persist. There must be, 
therefore, an abundance of fresh air playing about the 



THE WATER-COST OF DRY MATTER 131 

plant. Mineral food, though taken up in small quanti- 
ties, is indispensable to plant-growth. Through the action 
of the mineral foods, the most complicated processes of 
the plant are initiated and completed. Finally, carbon 
assimilation and growth cannot proceed unless there is 
a sufficient supply of moisture in the soil. The heat and 
light factors cannot well be controlled by the farmer; 
the mineral food can be controlled in part, but under con- 
ditions of irrigation the moisture environment of plant 
roots may be rather easily controlled. It is of first impor- 
tance, therefore, to the irrigation farmer, to know in what 
way variation in the moisture supply will affect the total 
production of dry matter of the crop he is growing. 

96. The transpiration ratio. — Dry matter is that 
part of a plant which remains when all the water has 
been driven off by heat near the temperature of boiling 
water. It is the only part of a plant of real value to the 
farmer in disposing of his crops for purposes of food, 
clothing or shelter, for the water contained in vegetable 
substances is of little more value than water drawn from a 
stream. The quantity of dry matter produced is, more- 
over, the best agricultural measure of the sum of the activi- 
ties of a crop during the growing season. 

The water-cost of the dry matter of plants may be 
expressed in various ways. The simplest and most easily 
understood, for the purposes of this chapter, is to speak 
of the number of pounds of water used in the production 
of one pound of dry matter. This method of expressing 
the water-cost of dry matter has been adopted by most 
investigators of the subject, and it is, therefore, well 
established. 

The pounds of water required for one pound of dry 
matter, may, however, be determined in two ways. Water 



132 



IRRIGATION PRACTICE 



is taken up by the roots, passed through the plant and 
evaporated at the leaves throughout the season. The 
pounds of water thus actually passing through the plant 
for each pound of dry matter produced, give the trans- 
piration ratio. Under agricultural conditions, however, 
as water passes through the plant, some water is also 
evaporated from the soil surrounding the plant. This 

direct loss from 
the soil surface, 
if completely 
checked, would 
seriously hinder 
plant-growth. The 
pounds of water 
passing through 
the plant and 
evaporating from 
the soil belonging 
to the plant, for 
each pound of dry 
matter produced, 
give the evapo- 
transpiration ratio. Students of this subject have not 
always carefully distinguished between these ratios; con- 
sequently, in modern agricultural books, the two ratios 
are found in the same tables as meaning the same thing. 
Of the two ratios, the evapo-transpiration ratio is more 
nearly the measure of the true agricultural needs of the 
plant. 

In the earlier investigations of the water-cost of dry 
matter it was dimly thought that, possibly, under all 
conditions, an invariable relationship existed between 
the quantities of water transpired and of dry matter pro- 




Fig. 23. Stomatal apparatus in carnation leaf 
through which transpiration occurs. 



THE WATER-COST OF DRY MATTER 



133 



duced — that the transpiration ratio would always be the 
same. If the increase in dry matter were thus always pro- 
portional to the quantity of water transpired, it would 
simplify greatly many important problems of agriculture. 
Such a definite relationship, however, was not found, and 
it is now well known that every agricultural practice 
influences not only the assimilation of carbon but, also, 
transpiration, though not always to the same degree or 
in the same direction. Transpiration and the production 
of dry matter are only in part interdependent; to a much 
larger degree they are independent of each other. This 
is a fundamental thesis of irrigation agriculture. 

Many investigators have determined the number of 
pounds of water required for the production of one pound 
of dry matter of various crops on a variety of soils and in 
several countries of the world. Some of these determina- 
tions are collected in the following table: 





Transpiration ratio 


Evapo-transpiration 
ratio 




England. 
Lawes & 
Gilbert 


>» 0> 

a m 

c3 Hi 

II 

(-. — i 
0> 0> 

Offi 


A 
S3 

P 


73 0> 

M * 

C3 o 


.9 


S3 


c >> 

o3 a 


Wheat 


247 


338 


546 


850 




1,017 




Barley 


257 


. , 




680 


464 




774 


Oats 




376 




870 


504 




665 


Corn 






386 


450 


270 


552 


233 


Clover 


269 


310 






577 






Peas 


259 


273 


843 


830 


477 


1,118 


416 



It may be noted that the transpiration ratios are lower 
in England and Germany, under humid conditions, than 
in Utah and India, under arid conditions. This is a general 



134 



IRRIGATION PRACTICE 



rule. Further, the transpiration ratios vary considerably, 
even under similar conditions of humidity or aridity, 
varying from 247 to 870 pounds of water for one pound 
of dry matter. As would be expected, the evapo-transpira- 
tion ratios are higher than the transpiration ratios. The 
variation among the evapo-transpiration ratios is also 
large, varying from 270 to 1,118 pounds of water for one 
pound of dry matter. 

The data in the above table may well be used to show 
the average limits of the magnitudes of the transpiration 
and evapo-transpiration ratios on good soils of the stand- 
ard crops in different parts of the world ; for, of the thou- 
sands of determinations, not included in the table, nearly 
all fall within the limits here given. Yet, in a given locality, 
the transpiration ratio is not even approximately constant, 
unless the many factors concerned in plant-growth and in 
evaporation are constant. The variability of the water- 
cost of dry matter is well brought out in the following 
table, which shows the range of transpiration ratios for 
certain standard crops in India and in Utah: 

Transpiration Ratio 



Crop 


India. 
Leather 


Utah. Widtsoe 


Wheat 


422-1,133 
490-1,117 
422- 679 
246- 804 
453- 973 


258-2,017 


Oats 




Barley 




Corn 


151-1,012 


Peas 


269-1,658 







For wheat, the range was in India from 422 to 1,133 
pounds of water, and in Utah from 258 to 2,017 pounds of 
water for each pound of dry matter produced. Other 



THE WATER-COST OF DRY MATTER 



135 



crops varied in very much the same manner. Whether 
countries or various fields of the same crop in the same 
country are compared, the water-cost of dry matter will 
vary widely. 

Meanwhile, under conditions of normal fertility and 
a favorable growing season, the transpiration ratios fall 




Fig. 24. Determining the transpiration ratio. 



within rather definite limits. In fact, under normal con- 
ditions, the evapo-transpiration ratio varies from 250 to 
1,000 pounds of water for each pound of dry matter. This 
gives a basis for an estimate of the quantity of water 
required for the production of a good crop of wheat or 
other standard crops. For example, a crop of wheat 



136 IRRIGATION PRACTICE 

yielding thirty bushels of grain to the acre, if 250 pounds 
of water are required for one pound of dry matter, would 
require throughout the season 5 acre-inches of water; if 
500 is the transpiration ratio, 10 inches would be required, 
and if 1,000 is the transpiration ratio 20 inches would be 
required. A fair crop of wheat requires annually, con- 
sidering the quantity that evaporates directly from the 
surface, from 5 to 20 inches throughout the season. This 
then gives a fairly safe basis on which to establish a 
duty of water. 

97. The seasons. — The seasons, including sunshine, 
temperature, relative humidity and all other climatic 
factors, are of first importance in determining the acre- 
yield of crops. In fact, for the production of dry matter, 
the seasons overshadow any other one natural factor, and 
usually is as important as the cultural operations. In 
irrigated sections, where water is added at will, the 
influence of the season is usually underestimated, for on a 
good and well-tilled soil, even though the season is unfa- 
vorable, the application of a sufficient quantity of water 
makes the crop sure. Nevertheless, in the irrigated sec- 
tions, as elsewhere, the seasons determine the average 
crop-yields for the season, whether they shall go high or 
fall low. 

The seasons also determine in large measure the quan- 
tity of water used in the production of one pound of dry 
matter. At the Utah Station, in a series of experiments 
covering several years, it was found that, under con- 
ditions otherwise nearly identical, the transpiration 
ratio for wheat varied from season to season, the range 
being from 280 to 577. In 1902, the transpiration ratio 
for wheat was 402; in 1903, 284; in 1904, 577; in 1905, 280, 
and in 1908, 357. Leather, working under East Indian 



THE WATER-COST OF DRY MATTER 137 

conditions, obtained similar results. The transpiration 
ratio of wheat varied from season to season from 507 
to 883, and of corn from 332 to 477. Both the Utah and 
the Indian experiments showed, for all crops investiga- 
ted, a similar seasonal variation in the water-cost of dry 
matter. Whenever the season is favorable for the produc- 
tion of much dry matter, the water-cost is reduced; that 
is, a good season produces not only a large yield, but pro- 
duces it with a relatively small quantity of water. A 
poor, backward season not only produces a small quantity 
of dry matter, but produces it at a high water-cost. The 
variation in the water-cost of dry matter, with the sea- 
sons, is much less than that of the total yield, as determined 
by the seasons. The water-cost is, however, influenced 
materially by the general seasonal conditions. 

98. The soil. — The vital relation of the soil to crops 
would naturally suggest that the quantity of water 
required to produce one pound of dry matter would be 
partly determined by the nature of the soil. This has been 
conclusively demonstrated by many elaborate investiga- 
tions. Pagnoul, working in France, found that the trans- 
piration ratio of fescue grass on a fertile soil was 555; on 
an infertile soil, 1,190. In the Utah experiments, the 
transpiration ratio for corn was 386 on College loam, 408 
on Sanpete clay, 561 on sand, and 601 on clay. Similar 
variations, some much larger, were observed with other 
crops on similar soils. For corn, the transpiration ratio 
varied, according to the soil used, from 432 to 579; for 
wheat, from 466 to 849. Similar results could be quoted 
in great abundance to substantiate the statement that 
the nature of the soil is a determining factor in the 
relative quantity of water used by the plant for the 
production of a given quantity of dry matter. 



138 IRRIGATION PRACTICE 

The physical and the chemical properties, as well as 
the depth of the soil, are of importance in determining the 
water-cost of dry matter. The deeper the soil is, the 
smaller is the transpiration ratio. This is to be expected, 
for the deeper the soil the more complete will the root- 
development be; and the more extensive the root-system 
is, the more easily may water and the mineral foods be 
obtained. Thus, carbon assimilation and all the other 
vital functions of the plant are stimulated into action. 
Leather grew crops in jars of different sizes, and, almost 
invariably, found that the crops grown in large jars 
were produced at the smallest water-cost. While the 
depth of the soil is an incidental factor, it may at times 
be of considerable importance. There is, throughout the 
irrigated region, a tendency to use very large quantities 
of seed. Unless the soil is deep and easily penetrated, the 
mass of roots, resulting from the large quantity of seed, 
may not find sufficient space in which to develop prop- 
erly. The resulting crowding and overcrowding lead to 
immense numbers of stunted individual plants, that do 
not always possess the vigor to use water to the best 
advantage. This is of particular importance wherever 
hardpan is near the surface, or where a heavy clay under- 
lies the top soil. Moderate quantities of seed should be 
sown, even under irrigation. 

The relation of the physical composition of a soil to 
the water-cost of the plant grown has not been thoroughly 
investigated. It was observed, however, long ago, that 
in the use of water, a loam soil is more economical than 
a sand soil. It seems that, with given conditions of 
fertility, the finer the soil the smaller is the transpira- 
tion ratio. Soils rich in clay or fine sand are naturally 
more economical of water than are those containing coarse 



THE WATER-COST OF DRY MATTER 139 

sand or poor in clay. However, the fertility of the soil, 
as expressed in plant-food content, or in good structure, 
seems to be of more importance than the texture of the 
soil. Any fertile soil, of whatever texture, will produce 
dry matter at about the same cost of water, providing all 
other factors are approximately the same. 

99. Mineral food or soil fertility. — The fertility of a 
soil, especially as measured in mineral food, is a large 
determining factor in the water-cost of dry matter. It 
has been shown in Chapter VI that transpiration is 
affected by the dissolved mineral constituents of the soil. 
The actual quantity of water required to produce one 
pound of dry matter is, likewise, materially influenced by 
the mineral plant-food in the soil. In practically every 
investigation, from the first to the latest, soils rated as 
fertile, because of their large annual yields, invariably 
yielded dry matter at a lower water-cost than less fertile 
soils. This law, that crops grown on fertile soils are pro- 
duced at a lower cost than those grown on an infertile 
soil, has been especially brought out by the diminished 
water-cost of crops grown on soils to which commercial 
fertilizers have been applied. The Utah experiments 
showed that, on moderately fertile soils, the transpiration 
ratio could be varied from 247 to 639 by applying very 
small quantities of commercial fertilizers. On two very 
infertile soils, the transpiration ratio due to fertilizers was 
reduced, in the case of the sand from 1,012 to 459, and in 
the case of the clay from 1,331 to 445. Soils of high fer- 
tility, however, did not respond to the application of 
fertilizers so far as the water-cost of dry matter was 
concerned. Leather, working under Indian conditions, 
came to the conclusion that suitable manures enable plants 
to economize water in the production of dry matter As 



140 IRRIGATION PRACTICE 

an average of many experiments, crops were produced on 
unmanured soils with a transpiration ratio of 782; and on 
manured soils with a transpiration ratio of 572. Bouyoucos 
has concluded, from a series of carefully conducted tests, 
that the greater the concentration of the soil solution, 
that is, the more substances it holds in solution, the 
smaller the transpiration ratio. Fertile soils are usually 
more soluble than infertile ones, and the soil solution of 
fertile soils is usually more concentrated. The same 
investigator has also shown that as the soil solution 
becomes richer in soil constituents, the cell sap of the 
plant becomes more concentrated, and that this may be 
the reason that less water enters the plant daily when 
the concentration of the soil solution is high. 

Different substances influence the transpiration ratio 
differently. Acids, for instance, tend to accelerate trans- 
piration, and to increase the transpiration ratio. Alkalies 
have the opposite effect. This is of importance to the 
irrigated sections, since under arid conditions alkaline, 
rather than acid, soils are naturally produced. Lime, 
phosphoric acid, potash and nitrates tend, especially, 
to reduce the water-cost of dry matter. Of first impor- 
tance are the nitrates. The richer the soil is in nitrates, 
the more surely will the water-cost of the crop be reduced. 
This law appears and reappears in investigations on all 
manner of soils, from all parts of the world. The main- 
tenance of an abundance of nitrates in the soil is undoubt- 
edly of prime importance in reducing the water needs of 
crops. Increasing the concentration of the soil solution 
reduces the transpiration ratio only when the substances 
held in solution in the soil moisture are true plant-foods. 
Bouyoucos showed that a solution of common salt, or 
sodium sulfate, or other substances, not direct plant- 



THE WATER-COST OF DRY MATTER 141 

foods, reduced the rate of transpiration, but did not 
diminish the water-cost of the resulting dry matter. It 
does not follow, therefore, that on alkali soils, such as 
occur frequently in the arid West, crops may be produced 
at a lower water-cost than on soils containing less soluble 
matter. Whether or not water is saved depends entirely 
upon the composition of the alkali. In places, the alkali 
consists largely of nitrates, potassium salts and other plant- 
foods; but, ordinarily, alkali lands contain the chlorides, 
sulfates and carbonates of sodium and other substances 
of a non-nutrient character. Crops grown on the usual 
alkali lands are not only injured by the high concentra- 
tion of the soil solution, but they are produced at an exces- 
sive cost of water. 

The irrigation farmer who wishes to make the best 
use of a limited quantity of water must keep steadily in 
mind the necessity of maintaining the soil, constantly, 
in a very fertile condition. 

100. Cultural operations. — It is well understood that 
thorough plowing, frequent cultivation and other correct 
cultural operations accelerate soil solubility and favor 
bacterial activity in the soil. Nitrification, the conversion 
of the soil nitrogen into nitrates, is especially fostered by 
proper soil tillage. This treatment given soils should, 
therefore, affect quite distinctly the water-cost of crops. 
Few experiments have been made on this subject, but 
those available bear out this belief. At the Utah Sta- 
tion, a number of pots containing soils of varying degrees 
of fertility were sown to corn. Half of the pots were 
properly cultivated, and the others received no culti- 
vation, throughout the growing season. The transpira- 
tion ratio was invariably smaller on the cultivated than 
on the non-cultivated soils. On College loam, the ratios 



142 IRRIGATION PRACTICE 

on the cultivated and on the non-cultivated pots were 
252 and 603; on a sandy clay, 428 and 535, and on an 
infertile clay, 582 and 750. It so happened that the Col- 
lege loam was a self-mulching soil, on which ordinary 
cultivation did not lessen direct evaporation. The favor- 
able effect of cultivation was shown, however, in the great 
reduction in the water-cost of dry matter resulting from 
simple tillage. On every hand the proper cultivation 
of the soil is shown to be a means of economizing water. 
It prevents the direct evaporation of water from the soil; 
it reduces the transpiration, and it makes it possible to 
produce dry matter at a low water-cost. There is much 
truth in the statement of the irrigation farmer that culti- 
vation may take the place of water. Within certain limits, 
it may be said that tillage is water. Water is indispensa- 
ble for the production of crops, but the need for water 
may be tremendously reduced if the upper layer of soil 
is thoroughly cultivated. 

All other correct treatments of the soil have pretty 
much the same effect. At the Utah Station, a series of 
soils were cropped every year for three years, while another 
similar series, receiving identical treatment, were left 
bare for three years. The fourth year, all the soils were 
planted to corn. The soils that had lain fallow for three 
years invariably produced dry matter at a lower water- 
cost than did those which has been cropped. The trans- 
piration ratios for the fallow and the cropped soils were, 
on the College loam, 573 and 659; on Sanpete clay 550 
and 889, on clay 1,739 and 7,466. Irrigated soils are 
cropped every year, and fallowing is scarcely ever prac- 
tised under irrigation. In fact, none of the established 
systems of irrigation-farming include the fallow year. 
Under dry-farm conditions, on the other hand, fallow- 



THE WATER-COST OF DRY MATTER 143 

ing is almost indispensable. Fallowing may be replaced 
by crops such as corn or sugar beets, which receive culti- 
vation throughout the season and thereby set free plant- 
food for the following crop. It is probable, however, that, 
even under conditions of irrigation, as in the West, 
where land is plentiful and water scarce, it may in the 
end be profitable to observe the occasional clean fallow of 
the land. The resting period not only helps to destroy 
weeds, plentiful under irrigation, but enables the soil to 
resume a natural physical condition, to set free plant- 
food and to start again a favorable bacterial flora. The 
value of fallowing is well shown is another of the Utah 
experiments. One series of soils had been cropped steadily 
for four years; another series had been cropped only three 
out of four years, and still another series had been cropped 
only one year out of four. These three series of soils were 
left exposed to the elements for three years; that is, they 
received a three-years' fallow. They were then all sown 
to corn, which grew and flourished well. The transpira- 
tion ratios, determined for each series of soils, were almost 
identical. This shows that the three years of fallow had 
restored the three soils to an approximate equality of 
fertility, so far as water-consumption was concerned, 
although at the beginning of the period, they had been 
left widely different by the various treatments they 
had received. The fallow period, objectionable chiefly 
because of the chance it gives the organic matter to be 
oxidized by the air, has great advantages in restoring the 
soil to a condition where crops may be produced at a low 
water-cost. 

101. The vigor of the plant. — Whenever the seasons, 
the nature of the soil, the available plant-food, the treat- 
ment of the soil, the factors above discussed, favor vigor- 



144 IRRIGATION PRACTICE 

ous plant-growth, they also tend to diminish the quantity 
of water required for the production of one pound of dry 
matter. That is, so far as these factors are concerned, as 
the plant becomes more and more thrifty the smaller 
becomes the transpiration ratio. The more vigorous a 
plant is, the more economically can it use the water at 
its disposal. 

102. Varying quantities of water. — Of greatest impor- 
tance in the consideration of the economical use of water 
by plants is the effect of varying quantities of water. 
Under irrigation, much or little water may be applied 
at the will of the farmer. Upon the proper manipulation 
of this characteristic factor, irrigation agriculture will 
stand or fall. It is, therefore, of prime importance to 
know how the production of crops is affected when the 
quantity of water applied is varied. 

Many experiments on this subject have been made 
lately, but not enough to set forth fully the principles 
involved. Most of the leading students of water in rela- 
tion to agriculture have lived in humid countries, where 
the only important control of soil water is the conserva- 
tion of the rain — or snow-water — in the soil upon which 
it falls. Only in recent years nas serious attention been 
given to the subject from the direct point of view of irriga- 
tion. Moreover, most of the experiments on this subject, 
many of high value, have been made in pots, under con- 
ditions not strictly comparable with the conditions of 
practical irrigation. Usually, the soils have been main- 
tained at definite degrees of wetness. To maintain these 
conditions, water was added to the pots every day or 
every few days, so that it could be said, at the end of the 
experiment, that the soil had been kept practically at 
that degree of saturation throughout the whole experi- 



THE WATER-COST OF DRY MATTER 145 

mental period. Under irrigation, the method is quite 
different, for the water is applied at relatively long inter- 
vals, and when the available soil moisture has been largely 
removed by the growing crop. The saturation of the soil 
falls, therefore, from high to low, between successive 
irrigations. 

All experiments on the subject, whether in pots or in 
the field, show that, as a general rule, the more water 
offered the plant, within practical limits, during the grow- 
ing season, the larger the total yield of dry matter. The 
increase in dry matter due to the increase in soil-saturation 
falls upon every part of the plant — roots, stems and leaves. 
Von Seelhorst and Tucker, among the early experimenters 
in this domain, showed, in a series of carefully conducted 
tests, that the whole oat plant — heads, straw and roots — 
increased as the water in the soil increased. In the pots con- 
taining a low percentage of water, 591 grams of the whole 
plant were obtained ; in the pot with a medium percentage 
of water, 725 grams, and in the pots with a high percent- 
age of water, 922 grams. In most experiments, only the 
parts of the plants harvested by the farmer are considered, 
so that this experiment is of special importance. The 
increase in the total yield of dry matter does not, however, 
continue indefinitely, as the soil-saturation increases. 
Mayer, who was one of the first to study the effect of 
varying quantities of water, found that for rye, wheat, 
barley and oats, the yield increased with the increase in 
soil-saturation up to a certain point, after which there 
was a strong diminution in the yield of dry matter. Experi- 
ments made elsewhere bear out this conclusion. As a 
further general rule, then, increasing the soil moisture 
increases the production of dry matter only within cer- 
tain definite limits. If too much water is applied to the 
J 



146 IRRIGATION PRACTICE 

soil during the season, there is a diminution instead of 
an increase in the yield obtained. 

This question, however, remains: As the dry matter 
increases with the increase in soil saturation, does the 
water-cost of each pound of dry matter remain the same? 
This matter has been investigated with considerable 
care and with concordant results. Wilms found that 
with a little water the transpiration ratio for potatoes 
was 39; with more water, 50; and with much water, 61. 
The Utah experiments showed invariably that with wheat, 
sugar beets, corn, potatoes, alfalfa and all other crops 
tested, as the quantity of water used was increased and 
the yield thereby increased, the water-cost also became 
larger. The general law is that, within the limits of 
practical irrigation, the transpiration ratio increases as 
the quantity of water added to the soil increases; that is, 
that the water-cost of crops becomes larger as more water 
is used in irrigation. Lyon and a number of his co-workers, 
notably Morgan and Harris, as well as other students, 
have confirmed this law, until it may be accepted as 
being securely established. This is a matter of tremend- 
ous importance. By using more water, the irrigation 
farmer obtains a larger yield, but less for each unit of 
water used. The question will always be, With how much 
water will he get the largest possible returns from the 
use of his land, water and labor? 

The only field experiments of any magnitude con- 
ducted with a view of testing the effect of various quan- 
tities of water on the production of dry matter and on 
the water-cost of dry matter are those of the Utah Sta- 
tion. Other experiments, not reduced to dry matter, will 
be noted in later chapters. In the following table the 
yields of dry matter in pounds to the acre, with varying 



THE WATER-COST OF DRY MATTER 



147 



quantities of water and on a deep fertile soil, are shown 
for four of the standard crops. The results are averages 
of a large number of experiments, and may be accepted 
as being tolerably accurate for the climate of the inter- 
mountain region. 

Yields of Dry Matter in Pounds per Acre with Varying 
Quantities of Water 



Inches of 
water applied 


Wheat 


Corn 


Sugar beets 


Potatoes 


5.0 


4,969 




6,080 


2,310 


7.5 


5,545 


10,757 


. 


2,730 


10.0 


5,684 


12,762 


8,053 


2,925 


15.0 


6,279 


13,092 


8,636 


3,405 


20.0 




13,856 


10,076 


4,005 


25.0 


6,672 


14,606 






30.0 




15,294 


10,271 


3,660 


35.0 


7,229 






. 


50.0 


7,999 




11,528 


*3,795 


55.0 




12,637 


. . . 


. . . 



*45 inches. 

An examination of the above table will show that as 
the quantity of irrigation water was increased throughout 
the season, the yield of wheat increased without inter- 
ruption; the corn increased up to 30 inches, but fell at 
55 inches; the sugar beets and the potatoes increased 
without interruption. This is in accordance with the law 
above stated that, as water is increased the general ten- 
dency of the yield of crops is to increase. The soil was deep 
and porous, into which even very large quantities of water 
sank to great depths. Thus, the soil was never over- 
saturated, but with large irrigations the soil-water film 
continued longer to be of maximum thickness than with 
small irrigations. Even under these favorable conditions, 
the yield of corn diminished after 30 inches of water had 



148 



IRRIGATION PRACTICE 



been applied, and the yields of other crops, not given in 
the table, likewise diminished after certain limits had been 
reached. Undoubtedly, had more water been used than 
the maximum in the above table, or if the soil had been 
shallower or less fertile, there would have been a strong 
falling off in the yields of all the crops. 

In the following table the evapo-transpiration ratios 
of the above yields under varying applications are given: 

Pounds op Water Required to Produce One Pound of Dry 

Matter with Varying Quantities of Water 

(Evapo-transpiration ratio) 



Inches 












of water 


Wheat 


Corn 


Alfalfa 


Sugar beets 


Potatoes 


applied 












5.0 


856 






569 


1,136 


7.5 


869 


276 






1,136 


10.0 


948 


275 


621 


57 i 


1,255 


15.0 


1,038 


356 


977 


663 


1,411 


20.0 




416 


946 


682 


1,466 


25.0 


1,317 


474 


1,052 




. 


30.0 




527 


1,253 


889 


2,242 


35.0 


1,530 


. 




. 


. 


45.0 




. . 


. 




3,060 


50.0 


1,809 


. 


1,480 


1,186 




55.0 


• • 


1,087 


• ■ 




3,292 



Without exception, when small quantities of water 
are applied, the water-cost is low; as larger quantities are 
applied, the water-cost becomes greater and greater. By 
increasing the total quantity of water throughout the 
season, the evapo-transpiration ratio or the pounds of 
water for one pound of dry matter increased for wheat 
from 850 to 1,809; for corn, from 255 to 1,087; for alfalfa, 
from 641 to 1,480; for sugar beets, from 569 to 1,186, and 
for potatoes, from 1,136 to 3,292. While, therefore, there 
is a distinct increase in dry matter as more water is 



C 

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Cjji 












































































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r-~ ' 










































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J 






































t 




































































g 


*£* 




















% 














0<* 


y> 


















- 












•» 
* 
















w 


het 


L'— < 






























s 








































S * 
o 














































0. 


























































































£ 
































































































j 


r 


A 


9 


/ 


f 


£ 


> 


£ 


J 


J 


7 


J 


/ 


40 


i S 


Jo ' 


S3 



Depth of Irrigation Water Applied (Inches) 

Fig. 25. Yield of dry matter of cereals with varying quantities of water. 






I 



tsoo 






i 


1 


































































































































1 










V 














































3 








































V 1 








































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B 






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V* 




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V, 500 
























































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■5 


















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to 








































- — < 






Q ioo 





























1 













S K> fS SO ZS JO 35 40^ -4S so ss 

Depth of Irrigation Water Applied (Inches) 

Fig. 26. Yield of dry matter of cereals per inch of irrigation water. 



(149) 



150 



IRRIGATION PRACTICE 



applied, this increase is obtained at a distinctly higher 
water-cost. Moderate irrigations are always most eco- 
nomical. 

The same figures are presented in a more practical 
manner in the following table, in which are shown the 
yields in pounds of dry matter to the acre for each inch 
of irrigation water under varying total irrigations: 



Pounds 


of Dry Matter per Acre per Inch of Irrigation Water 


Inches 
of water 
applied 


Wheat 


Corn 


Alfalfa 


Sugar beets 


Potatoes 


5.0 


994 






1,216 


462 


7.5 


739 


1,434 


. . 


. . 


364 


10.0 


568 


1,276 


909 


805 


293 


15.0 


419 


873 


463 


576 


227 


20.0 




693 


418 


504 


200 


25.0 


267 


584 


344 


, , 


. . 


30.0 


B . 


510 


m . 


342 


122 


35.0 


207 


. , 


271 


. # 


. . 


45.0 




. . 


. . 


. . 


84 


50.0 


160 


m m 


199 


231 


. . 


55.0 




230 


• • 


• • 


• • 



It is clear from the data of this table that, so far as 
water is concerned, it is more profitable to use small than 
large quantities of water. As the total seasonal quantity 
of water increased, the acre-yield of dry matter, for each 
inch of irrigation water, varied for wheat from 994 to 
160 pounds; for corn, from 1,434 to 230 pounds; for 
alfalfa, from 909 to 199 pounds; for sugar beets, from 1,216 
to 231 pounds, and for potatoes from 462 to 84 pounds. 
These are tremendous reductions with increasing appli- 
cations of water, which of necessity must be considered 
in the establishment of a consistent practice of irrigation, 
having as its purpose the reclamation of the largest pos- 



THE WATER-COST OF DRY MATTER 



151 



sible area in the arid regions. However true it may be, in 
the humid regions, that the acre-yield is the all-important 
thing, in arid regions the yield to the acre-inch or to the 
unit of water is equally important. For each crop and 
given conditions, a point must be determined at which 
the highest possible returns may be obtained from the 
land, water and labor employed. (Figs. 25, 26.) 

103. Maximum yield with given quantity of water. — 
The relation of varying quantities of water to the yields 
of crops may be expressed also by showing the producing 
power of a definite quantity of water, say 30 acre-inches, 
when spread over 1, 2, 4 or 6 acres. This is done in the 
following table: 

Pounds of Dry Matter Produced by 30 Acre-Inches of Water 



Crop 


Spread over 


Ratio 


1 acre 


4 acres 


Wheat 


6,951 
15,294 

8,133 
10,271 

3,660 


22,180 
43,028 
32,072 
28,268 
10,920 


3.19 


Corn 


2.81 


Alfalfa 


3.94 


Sugar beets 


2.75 


Potatoes 


2.98 







When 30 acre-inches were made to cover 4 acres 
instead of 1 acre, the yield was increased for wheat nearly 
three-fold, for alfalfa nearly four-fold, for sugar beets 
nearly three-fold and for potatoes nearly three-fold. When 
it is considered that the development of the arid regions 
will depend upon the settlement of a dense population, 
requiring food, clothing and shelter, it is evident that 
irrigation water, the limiting factor of the prosperity of 
the region, must be made to produce the largest quan- 
tities of materials for food, clothing and shelter. The 
acre-yield, the criterion of humid regions, will retreat 










Fig. 27. Crop-producing power of 30 acre-inches (wheat) 




"50/fcnt 

OverOpe 
flcng 



Owe rfoo Acnes 



Over T£neerfcnec 



Fig. 28. Crop-producing power of 30 
acre-inchea (alfalfa). 



(152) 



THE WATER-COST OF DRY MATTER 153 

before the acre-inch yield, the criterion of irrigated regions. 
The understanding of this principle must be brought 
into the practices of the people, and must reshape the 
irrigation laws of the states and federal government, if 
the greatest prosperity shall be won for the West. In 
the day to come, it is probable that no farmer, though he 
own an abundance of water, will be allowed to use more 




90/<b-r 









Fig. 29. Crop-producing power of 30 acre-inches (sugar beets) 

than the quantity determined upon by the state as being 
the best. 

The evils of over-irrigation are many. In addition to 
those mentioned, it is shown in this chapter that the large 
acre-use of water may diminish the actual yield an acre, 
and invariably does make the crop more expensive from 
the point of view of the water used for each unit of dry 
matter. The permanence of irrigation-farming depends 
on the moderate, use of water. (Figs. 27-29.) 



154 



IRRIGATION PRACTICE 



104. The nature of the crop. — The nature of the plant 
is a factor in the economical production of dry matter. 
Little is as yet known as to the special properties of the 
plant that affect the water-cost of dry matter; but, it is 
certain that plants differ in their water requirements. A 
number of interesting results have, indeed, been obtained, 
as for example, Montgomery's observation that narrow- 
leaved corn uses less water to produce a pound of dry 
matter than does corn with wider leaves. Attempts have 
often been made to classify crops in accordance with 
their water needs, but seldom under irrigated conditions. 

Some crops always yield largely, others lightly. This 
differing power is inherent in the crops, and is generally 
beyond the farmers' control, for the variations in yield 
due to cultural methods are within rather narrow limits. 
The results of the Utah work has made possible the 
arrangements of the crops in the order of their acre- 
yield of dry matter, as in the following table: 



Order of acre-yield of dry 

matter, beginning with the 

highest 



1. Corn . . . 

2. Carrots . . 

3. Sugar beets 

4. Barley . . 

5. Alfalfa . . 

6. Oats . . . 

7. Wheat . . 

8. Potatoes . 

9. Onions . . 
10. Cabbage . 



Pounds of water for one pound of dry 
matter (evapo-transpiration ratio) 



474 

760 

786 

998 

1,052 

871 

1,317 

1,854 

(2,557) 

(4,248) 




With light, medium and heavy irrigations, the order 
was practically the same. Corn yielded the largest quan- 
tity of dry matter to the acre; Italian rye grass, the smallest. 



THE WATER-COST OF DRY MATTER 155 

To the irrigation farmer, a large yield, however, is of 
interest only if it is produced with little water. In the 
second and third columns of the preceding table, therefore, 
are shown the pounds of water required for one pound of 
dry matter, or the evapo-transpiration ratio, when 10 
and when 25 inches were used. The uniform variation 
is remarkable. There was a steady diminution in the 
evapo-transpiration ratio, from corn to the lowest yielder. 
In the case of the two exceptions, oats and wheat, and 
corn and carrots, the yields were almost identical. Only 
under the 25-inch heading was there a notable exception — 
that of oats. The variation, however, is so regular, over 
so large a range of crops, that it may be suggested, as a 
law, that the water-cost of dry matter varies inversely 
as the inherent power of the plant to produce dry matter 
per acre. That is, the crop that yields most largely pro- 
duces the yield at the lowest water-cost. It may be 
observed in this connection that the crops that yield most 
heavily with the least expenditure of water are those of 
the longest growing period. 

Summary. — The factors that determine the water- 
cost of dry matter fall into two classes: First, those 
like the season, nature of the soil, mineral food, tillage, 
vigor of plant and nature of plant, that favor the produc- 
tion of dry matter, and at the same time diminish the 
rate of transpiration and reduce the water-cost of dry 
matter; and, second, those, like the varying quantity of 
water, that favor the production of dry matter, but at 
the same time accelerate transpiration and increase the 
water-cost of dry matter. All these factors are o£ great 
importance in the establishment of practices for the 
economical production of dry matter, but, the last, the 
varying quantity of water, because it is under the easy 



156 IRRIGATION PRACTICE 

control of the irrigation farmer, and, because its effects 
are large, is of greatest importance. 

REFERENCES 

Bouyoucos, G. J. Transpiration of Wheat Seedlings as Affected 
by Soils, by Solutions of Different Densities, and by Various 
Chemical Compounds. Proceedings of the American Society 
of Agronomy, Vol. Ill, p. 130 (1911). 

Briggs, Lyman J., and Shantz, H. L. The Water Requirements of 
Plants. United States Department of Agriculture, Bureau of 
Plant Industry, BuUetins Nos. 284 and 285 (1913). 

Fortier, Samuel. Soil Moisture in Relation to Crop- Yield. Mon- 
tana Experiment Station, Ninth Annual Report (1902). 

Harris, F. S. Effects of Varying Soil-Moisture Content on Certain 
Properties of the Soil and on the Growth of Wheat. Cornell 
University, Doctor's Thesis (1911). 

Harris, F. S. Long versus Short Periods of Transpiration in 
Plants Used as Indicators of Soil Fertility. Proceedings of the 
American Society of Agronomy, Vol. Ill (1910). 

Khankhaje, P. S. Some Factors Which Influence the Water Require- 
ments of Plants. Journal American Society of Agronomy, Vol. 
VI, p. 1 (1914). 

King, F. H. The Physics of Agriculture. Second edition (1901). 

Leather, J. W. Water Requirements of Crops in India. Agricul- 
tural Institute, Pusa, Memoirs of the Department of Agricul- 
ture in India, Part I, Vol. I, No. 8, (1910); Part II, Vol. I, No. 
10 (1911). 

Mayer, A. Ueber den Einfluss Kleineren oder Grosseren Mengen 
von Wasser auf die Entwickelung einiger Kulturpflanzen. 
Journal fur Landwirtschaft, Band 46, S. 167 (1898). 

Montgomery, E. G. Correlation Studies of Corn. Nebraska 
Experiment Station, Twenty-fourth Annual Report, p. 109, 
especially p. 150 (1911). 

Montgomery, E. G., and Kiesselbach, J. A. The Relation of 
Climatic Factors to the Water Used by the Corn Plant. 
Nebraska Experiment Station, Twenty-fourth Annual Report, 
p. 91 (1911). 



THE WATER-COST OF DRY MATTER 157 

Morgan, J. O. The Effect of Soil Moisture and Temperature on 
the Availability of Plant Nutrients in the Soil. Proceedings 
of the American Society of Agronomy, Vol. Ill, p. 191 (1911). 

Seelhorst, C. Von, and Tucker, G. M. Der Einfluss, welcher der 
Wassergehalt u. s. w. auf die Ausbilding der Haferpflanze, 
Journal fur Landwirtschaft, Band 46, 52 (1898). 

Widtsoe, J. A. The Chemical Life History of Lucern. Part I. 
Utah Experiment Station, Bulletin No. 48 (1896). 

Widtsoe, J. A. Factors Influencing Transpiration and Evaporation. 
Utah Experiment Station, Bulletin No. 105 (1905). 

Widtsoe, J. A. Dry-Farming. Chapter IX (1911). 

Widtsoe, J. A. The Production of Dry Matter with Different 
Quantities of Irrigation Water. Utah Experiment Station, 
Bulletin No. 116 (1912). 

Willard, R. E., and Humbert, E. P. Soil Moisture. New Mexico 
Experiment Station, Bulletin No. 86 (1913). 



CHAPTER VIII 
CROP DEVELOPMENT UNDER IRRIGATION 

The total yield of a crop is, usually, of first impor- 
tance; but, frequently, a particular part of the plant 
commands a much higher value than some other part. 
Thus, the seed of wheat, oats, barley, rye, corn and the 
other grains, has a much higher value than the straw; 
and the tops of sugar beets have comparatively little 
value, while the roots bring high money returns. For such 
plants, it is as important to regulate the proportion of 
plant parts as to produce a large yield of the whole plant. 
The whole crop of alfalfa and the hay crops generally, is 
sold, but the nutritive value of the hay, per pound, 
depends on the relative proportion of the stalks and 
leaves, since the leaves are much more nutritious than are 
the stalks. The farmer prefers leafy plants, and it is 
important to know under what conditions of irrigation 
the largest proportion of leaves may be obtained. 

In yet another way is this matter important. The 
grains, the grasses and many other crops are harvested 
only for the parts above ground. The roots are left in 
the ground to decay and have no direct money value. 
The substances elaborated in the plant are rather easily 
moved from place to place, and, under certain cultural 
treatments, it is conceivable that much of the nutritive 
material of the plant may move into the roots and remain 
there when the plant is harvested. The farmer needs to 
know, therefore, under what conditions of irrigation the 

(158) 



CROP DEVELOPMENT UNDER IRRIGATION 159 

largest possible proportion of the material formed in the 
plants may be retained in above-ground parts which are 
harvested. In the case of root crops, the reverse is desired. 
The roots possess the highest value, the tops the smallest 
and therefore the largest possible proportion of the plant 
constituents should be found in the roots at the time 
of harvest. 

Moreover, it is of interest and often of importance to 
know in what way the general growth of the plant is 
affected by varying methods of irrigation. To understand 
thoroughly the principles underlying the art of irriga- 
tion, it is not sufficient to know how much crop by weight 
is produced by given quantities of water applied in given 
ways, but it is equally important to know in what way 
the various parts of the plant are affected in their growth 
by such variations in irrigation. 

105. Response to irrigation. — The plant responds 
quickly to irrigation. In irrigation, water is applied at 
infrequent intervals. At first the soil is very wet; then it 
gradually dries, until it reaches the lento-capillary point 
or even the wilting point; then it is again wet, again dry, 
and so on throughout the season. 

All the life processes of plants growing on irrigated 
land become very active as soon as water is applied to 
the soil. Under conditions of irrigation, therefore, the 
plant is somewhat intermittent in its growth. Assimila- 
tion and all other processes favoring growth are espe- 
cially rapid after each irrigation, gradually diminishing in 
intensity and almost ceasing before the next irrigation. 

In the Utah experiments, for instance, it was found 
that during the first week after irrigation of peas, more 
than 500 pounds of dry matter were added to the weight, 
and of oats, more than 700 pounds of dry matter were 



160 



IRRIGATION PRACTICE 



added to the acre. Such large gains, could not, of course, 
continue for any length of time without resulting in total 
yields far above the maximum for the crops in question. 

Many of the effects of irrigation are more clearly 
understood if it is "kept in mind that the crop responds 
readily to the application of water. 




Fig. 30. Effect of little, medium and much water on wheat. 



106. Proportion of roots. — The vigor and general 
condition of the plant depend largely upon the develop- 
ment of the root-system. In the early stages of growth, 
the plant uses most of the materials gathered from the 
air and soil for the development of large and numerous 
roots, which, radiating through the soil, may readily 
absorb water and plant-food. When the roots are well 
developed, carbon-assimilation by the leaves is hastened, 
and growth is rapid. Later in the life of the plant, root- 
growth becomes slower and slower, and the energies of the 
plant are more largely directed to the development of 
the parts above ground. When at last the stems are well 



CROP DEVELOPMENT UNDER IRRIGATION 161 

developed and a sufficient quantity of materials has been 
stored in the various plant organs, growth diminishes, 
flowers and, later, seeds are developed. This is the 
natural course of plant-growth. It is indispensable that 
in the beginning the plant be given every possible chance 
to develop its root-system. 

It has long been known that a dry soil is more com- 
pletely filled with roots than is a wet one. Under dry- 
farm conditions, for instance, wheat roots penetrate 
heavy clay soils to a depth of 8 feet or more. No special 
attention was at first given to this observation, because, 
under the humid conditions prevailing in the earlier inves- 
tigations of agriculture, there seemed to be no practical 
method of regulating the quantity of water in the soil 
during the growing season. The rain came as it willed, 
irrespective of the needs of the farmer. During the 
last few years, however, this matter has been given 
quantitative investigation. Von Seelhorst and Tucker 
found that, of the whole oat plant, including the under- 
and above-ground parts, when little water was used, 
about 13 per cent was contained in the roots; when 
much water was used, about 7.5 per cent was found 
in the roots. With barley, wheat, peas, and other simi- 
lar crops, it has likewise been shown that the total and 
relative weights of roots are largest when little water 
is used. In the Utah work, it was found that the propor- 
tion of sugar beets or potatoes to the parts above ground 
was not greatly affected by the quantity of water used. 
In fact, the tendency seems to be that specialized roots 
and tubers increase slightly in proportion to the whole 
plant as the quantity of water is increased. It may, 
however, be stated, as a law fairly well established, that 
the roots of plants, at least of annual plants, always form 

K 



162 IRRIGATION PRACTICE 

a larger proportion of the whole plant when the soil is 
kept somewhat dry throughout the growing season. The 
roots seem to go in search of water and food, when little 
is at hand, thus increasing the root-development. It does 
not follow that the actual weight of roots produced in 
dry soil is much larger than when produced in wet soil. 
The experiments conducted on the subject indicate 
that the total weight is somewhat larger in dry than in 
wet soil; but, the differences are not great and do not 
approximate the differences in the proportions of roots 
in the whole plant. 

Gain has conducted a number of especially valuable 
experiments on this subject and has come to the conclus- 
ion that, whenever little water is added, the main or 
primary roots are large and well developed, while the side 
or secondary roots are small and poorly developed. If 
much water is used, the main roots are smaller and the 
side roots become relatively larger. That is, with little 
water a much larger volume of soil is reached by the root- 
system than when much water is used. 

The lesson to the irrigation farmer is clear. A plant 
with a small root-system, poorly developed, cannot make 
as good use of the water added to the soil, or of the food 
in the soil, as can a vigorous plant. It is important, 
therefore, that as early as possible the root-system be 
made large and well developed. When this has been 
accomplished, water may be added in considerable quan- 
tities without the fear that plant roots are unable to make 
proper use of it. As intimated above, to develop a large 
root-system it is necessary to keep the soil only mode- 
rately wet in early spring. In districts where the winter 
precipitation is fairly large, deep irrigated soils are fairly 
well stored with moisture in the spring, at the time of 



CROP DEVELOPMENT UNDER IRRIGATION 163 

seeding. If irrigation is applied very early to such lands, 
the root-system is likely to be retarded in its growth, and 
the final crop-yield may be greatly reduced. On soils 
practically saturated, at planting time, from the winter 
rains and snows, the first irrigation should be postponed 
as long as possible so that a strong root-system can be 
developed to use fully the water applied plentifully later 
in the season. This doctrine has been confirmed by many 
experiments under true irrigated conditions. For instance, 
in districts where the winter precipitation is so high (say 
8 inches during the six months of fall and winter) that 
the soil to a depth of 10 to 12 feet is approximately 
saturated, no benefits result from irrigation immediately 
after sowing; and the effect of the first irrigation becomes 
greater as it is removed in time from the date of seeding. 

Naturally, however, where the climatic conditions are 
such that at seeding time the soil is not well filled with 
water, thorough irrigation immediately before or after 
planting would do much to insure a proper germination 
of the seeds and a more rapid development of the root- 
system. Even when this is done, the longer the first 
irrigation is postponed, the better it will be for the crop, 
which then can better develop its root-system. Let it 
not be forgotten by the irrigation farmer that, in a rela- 
tively dry soil, roots will develop faster and will go more 
vigorously in search of water and food. 

107. Proportion of leaves and stems. — The part of 
the plant above ground is also definitely affected by 
the quantity of water applied. As the water applied to the 
soil increases, the whole plant becomes longer. This is 
true with all the common crops, such as wheat, oats, 
barley, rye, beans and buckwheat. Every farmer has 
observed that in fields to which water is added abundantly 



164 IRRIGATION PRACTICE 

the grain and hay stand high, and often the grain crops 
become so tall that they fall over and give a great deal of 
trouble at harvest time. Similarly, it is commonly 
observed that with little water the crops are short. Under 
dry-farming conditions, where the rainfall is small, the 
wheat is usually so short that instead of binders, which 
cannot be used, headers are employed which simply cut 
off the heads of the grain leaving the high straw standing. 
Further, as irrigation water is increased, the clusters of 
seed-bearing heads increase in number. The general 
appearance of the plant, therefore, depends on the quan- 
tity of water added to the soil during the growing season. 

Of chief importance is the effect of varying quanti- 
ties of water upon the stooling of the grains, that is, the 
number of seed-producing stalks from one seed. The 
more water is used, the more profuse becomes the stooling; 
the less water is used, the less stooling occurs. This is of 
particular importance wherever the seed is the chief 
product at the harvesting. 

In practically every experiment conducted on this 
subject, however, it has been found that, while the length 
of the plant and the number of seed-bearing stalks increase 
as the water increases, there is a limit to this correlation. 
The increase due to the increased irrigation continues only 
up to a definite limit, beyond which, if more water is 
added, a diminution occurs and the plant becomes shorter, 
the seed-bearing stalks less developed and with fewer 
seeds, and growth is arrested. A medium quantity of 
water would therefore be better than a very large quan- 
tity to produce large plants with many seeds. 

The nature of the leaves is influenced by the applica- 
tion of water. With little water the leaves of the grains 
are distinctly green and firm; with much water, they are 



CROP DEVELOPMENT UNDER IRRIGATION 165 

pale green and soft. In the case of corn, it has been shown, 
also, that with little water the leaves are narrow and 
pointed, whereas with much water they are wide and 
more rounded, and their screw-like turning increases. 
Wilms showed that, in the case of potatoes, a small amount 
of water produced a thick leaf containing long cells and 
few stomata or breathing pores per square inch, while 
much water produced thinner leaves containing short 
cells and many more stomata per unit of surface. That 
is, in color, form, consistency, cell-structure, and other 
properties, both the leaves and the stems respond definitely 
to varying quantities of water. This emphasizes the power 
of the irrigation farmer, by merely varying the quantity 
of water applied to plants, to change the color of the plant, 
the stiffness of the stalks, the shape of the leaves, and 
many other similar properties. Every part of the plant is 
changed to correspond with the water at the disposal of 
the plant. 

Of more direct interest, however, to the farmer, than 
the size and shape, is the relative proportion of leaves, 
stalks or other parts of a crop. The leaves of plants, 
whether large or small, are usually of higher nutritive 
value than the stalks. It is desirable therefore, when a 
crop is grown for forage to secure the largest proportion 
of leaves. The few available investigations make it clear 
that the proportional parts of leaves and stalks are dis- 
tinctly affected by the quantity of water used in irriga- 
tion. In the Utah experiments, with wheat, oats and peas, 
the proportion of leaves in the whole plant became higher 
and higher as the water was increased, whereas with 
potatoes the reverse occurred. When the leaves and 
stalks alone were compared, it was found that, as with 
potatoes, the less water used the leafier were the plants. 



166 IRRIGATION PRACTICE 

In general, much water produces at first leafy plants; 
if more is added, the proportion is diminished. Crops 
grown for forage, in which a high proportion of leaves is 
desirable, may profitably be given larger quantities of 
water than crops that are grown more largely for some 
other part of the plant. 

108. Proportion of heads and grain. — The grain 
crops are grown primarily for seed. The value of the 
straw is small in comparison with that of the seed. The 
grain farmer desires therefore to convert as much as pos- 
sible of the plant into seed at the time of harvest. Up 
to a definite limit, the clusters of seed-bearing heads 
increase with the quantity of water used. The number 
of seeds in each head of wheat, or ear of corn increases, 
likewise, as the quantity of water is increased. Even 
the beard in the bearded varieties, becomes longer or 
shorter as much or little water is applied. The seed- 
bearing part of plants, like the roots, stalks and leaves, is 
sensitive to the water applied to the soil. 

Many reported experiments deal with the proportions 
of the heads in grain crops as influenced by varying 
quantities of water. In the Utah experiments it was 
found that as the total quantity of irrigation water was 
increased the proportion of heads in the plant above 
ground decreased with wheat, from 38 to 25 per cent; 
with oats, from 59 to 49 per cent; with peas, from 67 to 
48 per cent. In every case it was distinctly shown that 
the more water applied, the smaller the proportion of 
the heads in the whole plant. Therefore, while the size 
and number of heads seem to be increased as the total 
quantity of water increases, it is equally clear that the 
stems and leaves are increased more markedly. This 
leads to a decreasing proportion of heads in the whole 



CROP DEVELOPMENT UNDER IRRIGATION 167 

plant as the water applied increases throughout the 
season. 

This correlation has been demonstrated by a great 
number of investigators, although in few cases only 
under true irrigated conditions. Hellriegel was one of 
the first to investigate this subject and to announce the 
law that the proportion of seed to the straw in all ordi- 
nary crops becomes smaller as the available water in the 
soil during the growing season increases. Mayer, working 
in Holland, investigated rye, wheat, barley and oats, 
and found invariably that the more water he offered the 
plants, the smaller became the proportion of the grain 
yielded by the crops. French and English investigators 
have confirmed this conclusion. At the Utah Station, in 
a long series of experiments under irrigated conditions, the 
percentage of seed in the harvests of wheat, oats, barley 
and corn was very carefully determined. In the following 
table some of the results obtained are shown: 



Depth of 

water applied 

(inches) 


Percentage of grain in harvest of 


Wheat 


Oats 


Barley 


Corn 


5.0- 7.5 

15.0 

25.0-35.0 

45.0-50.0 


44.45 
40.83 
38.65 
32.89 


64.54 
62.55 

57.63 


50.74 
47.09 
38.27 


51.69 
47.92 
43.55 



In the first column is given the depth, in inches, of 
the water applied throughout the growing season; in the 
following columns, for each crop, the percentage of grain 
in the total harvest. The smallest quantity of water 
applied was 5 inches, and the largest 50 inches. The small- 
est quantity used should meet, fairly, ordinary crop needs, 
and the largest quantity used is not very far above that 



)pan 



^?ra. 



7.S /n> 

water 



is tn. 

water 



Z5 in 
water 



so /n 
water 



Fig. 31. Proportion of grain and straw with varying irrigations (wheat). 



(168) 



CROP DEVELOPMENT UNDER IRRIGATION 169 

actually used, though wastefully, in many of the irrigated 
sections. 

With the smallest quantity of water, nearly 45 per 
cent of the total wheat crop was seed; as the water was 
increased, the percentage became smaller and smaller, 
until, with 50 inches, the percentage of seed in the crop 
was less than 33 per cent. In a similar manner, the seed 
in oats fell from 64 to 57 per cent as the water was 
increased; in barley, from nearly 51 to a little over 38 
per cent, and in corn, from nearly 52 to about 43 per cent. 

That is, under irrigated field conditions, the law 
which has been so frequently determined in pot experi- 
ments has been fully confirmed: namely, as the water 
available to plants increases, the proportion of seed in 
the plants decreases. This is naturally of the deepest 
significance to the irrigation farmer, for not only does 
the total yield of the crop per unit of water decrease 
largely as more water is used, but the proportion of the 
more valuable parts of the plant decreases also. The 
meaning of this is that, if the yield per acre-inch of 
water of the whole wheat crop is diminished as more 
water is used, the yield of grain is even more largely 
decreased. The grain farmer cannot, therefore, by any 
process of reasoning convince himself that it is desirable 
to use very large quantities of water for the production 
of his crops. (Fig. 31.) 

It may be said, in this connection, that the prevail- 
ing idea that grain grown with little water is not so full 
and plump as that produced with more water, is erro- 
neous. This phase of the matter will be discussed in 
Chapter XI. 

109. Other plant parts. — The development of crops 
under the influence of irrigation as here outlined is fairly 



170 IRRIGATION PRACTICE 

well established and may be safely accepted, yet it is 
not to be forgotten that much work must yet be done 
with the various crops before a full knowledge of the 
subject is in our possession. We may say with a certainty 
that the leaves, stems, seeds and roots of crops are influ- 
enced definitely by varying the quantity of irrigation 
water. We do not know definitely, however, how the 
yield of fruit is affected by varying quantities of water, 
although in view of the high value of the fruit crop, this 
is a particularly important need. It is probably true that 
the production of fruit depends upon the time at which 
water is applied rather than upon the total quantity of 
water. However, from early springtime each tree sends 
forth its leaves, and the materials elaborated by the 
leaves are distributed throughout the whole tree — to 
develop roots, trunk and branches, and to produce fruit. 
Undoubtedly, the quantity of water applied plays an 
important part in determining how these elaborated 
materials shall be used in the tree. In so large a struc- 
ture as a well-matured fruit tree it must be of great impor- 
tance to know how the materials gathered from the soil 
and air may be driven into the fruit, without injuring the 
well-being of trunk, branches and roots of the tree. That 
the fruit crop is as sensitive as other crops to the effects 
of varying quantities of water is well shown in several 
experiments. For instance, Jones and Colver, in a study of 
the composition of irrigated and non-irrigated fruits, 
conducted under the auspices of the Idaho Experiment 
Station, and using fruit grown under the somewhat 
humid conditions of northern Idaho, found that the pro- 
portion of seeds, skins and other wastes of fruits was 
high or low as the fruit was or was not irrigated. The 
following table gives some of the results: 



CROP DEVELOPMENT UNDER IRRIGATION 171 



Edible portion 



Cherries, Bing . . . . 
Plums, Green Gage . . 
Prunes, Italian . . . . 
Apples, Arkansas Black 



Irrigated 



92.35 
87.57 
95.66 
91.49 



Non-irrigated 



87.30 
77.36 
93.00 
90.02 



It was further observed that the various parts of the 
waste varied with the water used. As our knowledge of 
this matter grows, it will no doubt be possible, under con- 
ditions of irrigation, to control largely the output of fruit 
from a given orchard. 

A similar problem is connected with the production 
of the tomato, which is grown in tremendously large 
quantities in districts where the canning factories operate. 
It is of prime importance to obtain the largest yield by 
weight of tomatoes, considering both quality, size and 
shape. To make the vines small and the tomatoes large is 
a question of very great importance. The same may be 
said of the cantaloupe industry, which assumes large 
proportions in certain sections of the irrigated West. 
The agricultural investigators of the irrigated regions 
must take these matters in hand at an early date, to dis- 
cover the laws that control the production of the various 
parts of all the crops that are commonly grown under 
irrigation. 

The length of season also has an important bearing 
upon the economy of the water used. By varying the 
quantity of water used, it is possible, at least in a small 
measure, to lengthen out or shorten the season. As is 
well known, the more water is at the disposal of the plant, 
the longer growth continues. If the soil moisture is high 
in early spring, there is a tendency for the plant to pre- 



172 IRRIGATION PRACTICE 

pare for a long wet season, and if this same environment 
is continued throughout the season, the plant continues 
the vegetative processes much longer than if the moisture 
from the earliest period is relatively low. In general, 
we may lay down the law that the more water used, the 
longer the growing season of the plant; the smaller the 
quantity of water used, the shorter its growing season. 
This may often find important applications. For instance, 
wherever early and late frosts prevail, the moderate 
use of water will hasten maturity; and, in hot, dry dis- 
tricts, the moderate use of water will prevent an unneces- 
sarily long vegetative period with rapid evaporation. 

REFERENCES 

Harris, F. S. The Irrigation and Manuring of Corn. Utah Experi- 
ment Station, Bulletin No. — (1914). 

Widtsoe, J. A. The Effect of Varying Quantities of Irrigation 
Water on the Production of Dry Matter. Utah Experiment 
Station, Bulletin No. 116 (1912). 

Widtsoe, J. A., and Stewart, Robert. The Effect of Irrigation 
on the Growth and Composition of Plants and Different Periods 
of Development. Utah Experiment Station, Bulletin No. 116 
(1912). 



CHAPTER IX 

THE TIME OF IRRIGATION 

Under ideal conditions of irrigation, a plentiful supply 
of water would always be at the disposition of the farmer. 
In practice, such a condition seldom exists. The flow of 
water in the rivers from which the canals are taken, varies 
from season to season, and, unless the water is stored in 
reservoirs, there is not, throughout the season, a uniform 
supply of water. In the spring, the flow is beyond the 
capacities of the canals; in midsummer and later it is 
often insufficient for the needs of the system. Different 
crops have different water requirements, both as to total 
quantity and periodic application. Young plants use less 
water than do the larger and stronger plants some weeks 
older; and the mature plant, the life activities of which 
have ceased, has very little need of water. The life his- 
tory of the plant determines, largely, the best time of 
irrigation. It seldom happens, however, that the periodic 
natural flow of water coincides with the periodic crop 
requirements. The problem of applying the best quantity 
of water at the proper time, which will determine the 
principles of canal management, is one of the most com- 
plex in irrigation practice. 

110. The ideal principle. — It may be laid down as 
an ideal principle, that, so far as possible, the same 
percentage of moisture should be maintained in the soil 
throughout the growing season, irrespective of the age 
of the plant. That is, the soil-water film should be kept 

(173) 



174 IRRIGATION PRACTICE 

at the same thickness while the plant is growing. The 
young plant requires less water per day than the older 
plant, but the ease with which the water may be obtained 
should be practically the same for young and older plants, 
as long as they are growing vigorously. Such a condition 
of uniform water content in the soil is practically impos- 
sible unless water is added daily to the soil to replace that 
lost by evaporation and transpiration. The intermit- 
tent nature of irrigation, fundamentally characteristic, 
implies a period of high moisture percentage imme- 
diately after an irrigation, gradually diminishing until, 
just before the following irrigation, the soil is often very 
dry. Nevertheless, the irrigation farmer must attempt to 
apply irrigation water in such a way as to leave the plant 
in an approximately uniform moisture environment 
throughout the season. Therefore, irrigation must be 
more abundant and frequent at periods of high transpira- 
tion. So far as the soil is concerned, the intermittent 
nature of irrigation is highly favorable in producing a 
condition favorable to plant-growth. 

The discussion of the time of applying irrigation water 
may be surveyed as follows: 

1. Irrigation when crop is not growing. 

(a) Fall irrigation. 

(b) Winter irrigation. 

(c) Early spring irrigation. 

2. Irrigation when crop is growing. 

(a) For germination. 

(6) Use of early spring floods. 

(c) Irrigation at different periods of crop growth. 

(x) Annuals. 

(y) Biennials. 

(?) Perennials. 



TIME OF IRRIGATION 175 

111. Fall irrigation. — Fall irrigation means irrigation 
after harvest, but before winter sets in. After harvest, 
water still flows down the river channels and ordinarily 
goes to waste. This late water may be used to saturate 
the soil, and thus be held over until the following growing 
season. In districts where the fall and winter percipita- 
tion is insufficient to saturate the soil, fall irrigation is 
especially desirable. 

An average soil of the arid regions, under field con- 
ditions, is saturated when it contains about 18 per cent of 
water to a depth of 10 feet. This is equivalent, approxi- 
mately, to a depth of 3 feet of water. Under wise systems 
of cropping, about 12 per cent of water is left in the soil 
to a depth of 10 feet at the time of harvest. At the follow- 
ing seed time, the soil should again be in a saturated con- 
dition. The difference between 12 per cent and 18 per 
cent, or practically 1 foot of water, should, therefore, be 
furnished by the natural precipitation, or by fall, winter 
or spring irrigation. 

Over a large area of the inter-mountain country, the 
precipitation comes chiefly in the fall and winter or early 
spring, that is, between harvest and seed time. In this 
district, fall and winter irrigation have little value, if the 
land is so treated as to permit the storage in the soil of 
the rain- and snow-water — unless the total seasonal 
precipitation is low, when irrigation during the fall sea- 
son may be very helpful. In other sections, much of 
the rainfall comes in late spring, summer or early fall, 
that is, during the growing season. This water does not 
remain stored in the soil during the winter for the use 
of next season's crop, and under this condition, fall 
irrigation is highly profitable. 

It is of great advantage to have the soil saturated 



176 IRRIGATION PRACTICE 

at planting time, for (1) it makes possible a quicker and 
more complete germination, and (2) it delays the time 
of the first irrigation, and the plant is enabled to estab- 
lish a strong root-system. It is, also, decidedly advanta- 
geous to keep the soil well saturated with water through- 
out the dormant season. Water added in the fall dis- 
tributes itself in the usual way throughout the soil to a 
considerable depth. The soil-water film then remains 
long in intimate contact with the soil particles; plant- 
food is dissolved and well distributed throughout the 
water until, at planting time, the soil-water is heavily 
charged with dissolved plant-food and is a very nutri- 
tious medium for plant-growth. 

Water applied during the growing season is imme- 
diately drawn upon by the plant, and does not remain in 
the soil long enough to permit of extensive solution or 
distribution of soil nutrients in the soil-moisture film. 
Only the portions of the soil-water film that lie nearest 
to the soil particles become rich in plant-food. This may 
be the one explanation of the repeated observation that 
a given quantity of water applied in irrigations at inter- 
vals of one, two, three or even four weeks may often 
yield a larger crop than when applied in smaller and more 
frequent irrigations. Water applied too frequently or in 
small quantities is pumped out of the soil so rapidly 
that there is little chance for solution of plant-food. 
With longer intervals and larger irrigations, more plant- 
food may be dissolved and used in plant-production. 

At any rate, water applied in the fall and winter sea- 
son has the opportunity throughout the long months of 
the dormant season to dissolve from the soil such materials 
as will be of value in plant-growth. Such soil solution is 
of tremendous value in establishing the young plant dur- 



TIME OF IRRIGATION 111 

ing the earlier periods of growth. Water stored in the 
soil at the time of planting is invariably more valuable, 
unit for unit, than water applied directly at the time of, 
or immediately after planting. 

Fall irrigation may be applied to bare lands at any 
time after harvest. The common practice is to apply the 
water as soon as may be convenient after harvest without 
previous plowing, and to allow the soil to remain unplowed 
until the following spring. Another practice is to plow 
soon after harvest and then to apply water. When the 
soil " washes" easily, this latter practice is not always 
successful; moreover, plowed land is irrigated with diffi- 
culty. The structure of some soils is easily injured by 
the work of making the water cover the plowed land, thus 
affecting the crop of the following year. On orchards, fall 
irrigation should not be applied too early. The soil 
should be allowed to become dry in the early fall, so that 
the trees may ripen their wood for the winter's rest. 
Then fall irrigation may be applied in safety. If water is 
applied to trees before growth has ceased, a late new 
growth is started, which usually results in winter-killing. 
Naturally, this applies only to deciduous trees. Citrus 
trees are irrigated during the whole year, if necessary. 

Generally, when fall irrigation is applied late enough 
it results only in good. Lands are not ordinarily culti- 
vated after fall irrigations, because, over the larger part 
of the irrigated territory, the fall rains usually leave the 
top soil in a condition to be puddled if subjected to tillage. 
However, a soil that has been fall-irrigated should be 
carefully cultivated in the spring, just as soon as the top 
soil is in the proper condition. It is never wise to use 
tillage implements on soils that are too wet. Early spring 
cultivation always means cultivation performed on a 



178 IRRIGATION PRACTICE 

soil sufficiently dry to support the tools without danger 
to the soil structure. 

Fall irrigation has been tried extensively in places 
where the winter rainfall is light, and almost invariably 
with great success. Wherever the winter precipitation is 
high, it is probably unnecessary and possibly inadvisa- 
ble to practise fall irrigation. Meanwhile, the use of the 
water which ordinarily goes to waste in the fall may be 
the means of making the summer flow cover a larger 
area of land than would otherwise be possible. 

112. Winter irrigation. — Winter irrigation means the 
application of water to the soil during the winter proper. 
It is seldom practised where the winters are closed in by 
snow or where the top soil is frozen for weeks or months. 
It is true that an unsaturated soil, when frozen, is of a 
granular structure, and that through such a frozen soil 
water penetrates to considerable depths. However, 
water applied to frozen soils stands on the soil and often 
freezes into sheets of ice. On bare soils this does little 
harm and little good. A possible advantage is that when 
the warmer weather melts the ice and opens the soils, 
the water that has not run off soaks rapidly into the soil. 
On lands bearing grass or lucern, great injury is done 
when sheets of ice are formed over the surface of the fields, 
and winter irrigation should never be practised on such 
fields where freezing weather characterizes the winters. 

Winter irrigation is and should be practised chiefly 
where the winters are mild and open. In such districts, 
winter irrigation is really a later fall irrigation. All the 
arguments in favor of fall irrigation hold for such winter 
irrigation. 

Excellent studies have been made of the value of 
winter or late fall irrigation in supplementing the rain- 



TIME OF IRRIGATION 179 

fall and increasing the duty of irrigation water through 
the growing season. The most notable of these studies 
was made in 1898 and 1899 by McClatchie, in an Arizona 
valley where the annual rainfall averages about 11 inches, 
and is so distributed as to be heaviest from July to Sep- 
tember and from December to February. Deciduous 
trees shed their leaves in November; the buds start in 
February, and the leaves are generally out by the end of 
March. Heavy frosts often occur in December and 
January. The orchard used for the experiments contained 
chiefly peaches and apricots planted in 1892. In 1898, 
the orchard was irrigated in September. Then, from 
January 2 to March 1, 1899, the orchard received eight 
irrigations. It was then plowed and harrowed. From 
March 31 to June 24, 1899, no further irrigation was 
applied and no rain fell during that time. In spite of the 
lack of irrigation the growth of the trees and the yield of 
fruit were excellent. On December 16, 1899, the winter 
irrigations began again and 3 acre-feet of water were ap- 
plied between that date and March 5, 1900. During the fol- 
lowing eight months no irrigation water was applied, and 
the rainfall during that period was only about 2^ inches, 
distributed among five rains. At the end of the eight 
months the trees were in fine condition and the yield of 
fruit was excellent. The season was the driest and hot- 
test on the records of the state. 

This classical experiment demonstrates conclusively 
the high crop-producing value of fall and winter irriga- 
tion, correctly applied in districts where such irrigation 
is at all practical. It reemphasizes also the doctrine that, 
when the soil is used as a storage reservoir, it is not neces- 
sary that much water be added during the growing sea- 
son of the crop. 



180 IRRIGATION PRACTICE 

McClatchie observed that, as a result of heavy win- 
ter irrigations, the tree roots grew while there was no 
visible growth above the ground. The strengthened roots 
then made possible rather rapid growth above ground at 
a later period. Roots were found plentifully to a depth 
of 16 feet and one was followed to a depth of 20 feet. 
Available moisture was observed to a depth of 20 to 25 
feet. The major use of water by the trees was in the 
spring and early summer. In the later summer the trees 
were somewhat sluggish so far as the use of water was 
concerned. As a result of his investigations, McClatchie 
advised the use of winter irrigation, and not to exceed 
one summer irrigation, for the successful production of 
fruit in that section of Arizona. 

It must not be believed, however, that under fall and 
winter irrigation plants are given less moisture than when 
the water is added in summer. More likely the liberal 
use of water in fall and winter, when few farmers use it, 
means that really more water is thus used for the produc- 
tion of dry matter. In the experiment above cited, it was 
found that approximately 48 inches of water were received 
throughout the season. This was used by the orchard 
proper, by the cover-crop for the maintenance of soil 
fertility, and by evaporation. Whether in winter or sum- 
mer, water should be used sparingly. ' 

Winter and fall irrigations are two excellent methods 
whereby the waters which now largely go to waste may 
be so conserved as to increase the duty of the summer 
flow. In time, as more reservoirs are built and all the 
fall and winter waters are held back in these reservoirs, 
fall and winter irrigation will not be so important; but 
even under these future ideal conditions, it may be found 
desirable to irrigate the soil in the fall, so that, in the 



TIME OF IRRIGATION 181 

spring, there may be an abundance of water, heavily 
charged with the valuable constituents of the soil, for 
the use of the young plant. 

113. Early spring irrigation. — This refers to irriga- 
tion made soon after the winter breaks, either before or 
after planting, but nearly always before the plant is really 
in need of additional water. When spring appears, the 
melting mountain snows increase greatly the river flow, 
culminating in the period of high water and spring floods. 
Unless reservoir provisions are made these great quan- 
tities of water flow away unused and it is an increasingly 
important question whether this spring flow may be 
diverted profitably upon cultivated lands. 

If the soil has been well filled with water during fall 
and winter, either by late irrigation or by heavy winter 
precipitation, it is probably useless to expect that spring 
irrigations will benefit crops. The early application of 
water may rather be detrimental in such places, as it 
tends to wash down, beyond the reach of plant roots, the 
rich soil solution formed during the winter. 

On the other hand, wherever the winters are dry, or 
where fall and winter irrigation cannot well be practised, 
the application of water in the early spring may be bene- 
ficial in stimulating early crop-growth. In fact, in local- 
ities where the soil in spring is in a condition too dry 
for germination, it is indispensable that water be applied 
to the soil about the time of planting, if any crop at all 
is to be obtained. In such districts, water is often applied 
to the soil some time before the planting season. After 
the water has distributed itself throughout the soil, the 
top soil is loosened to prevent evaporation and to furnish 
a good seed-bed. Usually, however, the seed is sown in 
the relatively dry soil and a rather heavy irrigation is 



182 IRRIGATION PRACTICE 

applied afterward. In either case, germination is 
encouraged. 

Our present knowledge leads to the belief that spring 
irrigation should be practised only where it is absolutely 
indispensable. The value of early irrigation depends 
upon the quantity of water in the soil in the early spring. 
It is much better, wherever conditions permit, to irrigate 
in the fall, and to conserve in the soil as much as possible 
of the natural precipitation, so that the seed may be 
planted without irrigation and the first irrigation may be 
postponed until early growth is well started, and late 
spring or early summer weather has set in. 

This matter was tried out at the Utah Station with the 
result that the longer the spring irrigation was postponed, 
the more valuable it became in increasing the crop-yield. 
Under the prevailing conditions, there was a liberal 
fall, winter and early spring precipitation, so that at plant- 
ing time the soils were usually saturated with water. To 
irrigate such soils does little good, and possibly results 
in harm. Only where germination will be delayed or be 
incomplete without irrigation should the early applica- 
tion of water be practised. It is of prime importance, for 
obtaining the best results, that the soil be well filled with 
moisture at the time of planting. 

114. Irrigation during growth. — The time to irrigate 
crops during their growth should measurably determine 
the rotation of water from irrigation systems and it bears, 
therefore, directly upon the question of canal manage- 
ment. 

In the spring, when the root-system is being developed, 
the growth above ground is slow. With each day, however, 
the rate of growth increases, until buds and flowers 
appear. At that time the rate of plant-growth is most 



TIME OF IRRIGATION 183 

rapid; and this rapid growth, or increase in weight, con- 
tinues during the whole time of early flowering. When 
seed-formation begins, the rate of growth diminishes; 
and after the seeds have been formed, it is even smaller 
than in the earlier stages. 

The water transpired by crops is generally, though 
not always, in proportion to the rate of growth. Water 
lost by evaporation from the soil increases and decreases 
largely in the same proportion, because the time, tem- 
perature and other conditions that determine the rate of 
plant-growth also determine the rate of direct evaporation. 

Such a coincident variation would mean that little 
water needs be applied in the earlier periods of plant- 
growth, but that, as the rate of growth increases, the rate 
of adding water must be increased until the period of 
seed-formation approaches, when the supply may again 
be diminished. In practice, it is exceedingly difficult even 
to approximate this ideal system of irrigation, for the 
stream flow in most localities decreases rapidly from early 
spring until the time of maximum water needs is reached. 
At that time of high requirements and low supply it is 
difficult for the farmer to supply his crops with the best 
quantity of water at the right time. Under reservoir con- 
ditions, the ideal requirements are more nearly met. 
Nevertheless, under any conditions, the farmer must 
attempt, as nearly as may be possible, to give his crops 
most water at the time when the crops need water most. 
This time, in turn, depends on the crops grown under the 
system. By a wise diversity of crops, a small stream in 
early or late summer may be made to served a large area 
well. 

115. Time of irrigating short-season crops. — Wheat 
and the other small grains, peas, beans and similar short- 



184 IRRIGATION PRACTICE 

season crops, after having been planted in a soil well 
filled with moisture, should be allowed to grow as long as 
possible without irrigation. The early irrigation of such 
crops is only slightly advantageous, and the results 
seldom pay for the labor and cost of water. By post- 
poning the first irrigation, the root-system may be more 
fully developed, so that the best use may be made of the 
water when it is applied. Such crops, grown for seed, 
seldom need irrigation before the time of flowering or 
seed-formation, when one or two moderate irrigations 
may be applied with decided advantage. 

At the Utah Station it was found that, when a given 
quantity of water was used, the total weight of the crop 
was not greatly affected by varying the time of irrigation; 
the effects were felt in the yields of grain produced. When 
irrigation was performed early, before flowering, more 
straw and less seed were produced; when irrigation came 
late, less straw and more seed resulted. The sum of- straw 
and seed was, in both cases, practically the same. That 
is, late irrigations make possible the transfer of nutritive 
materials from the roots and stalks to the heads, there to 
be permanently elaborated into seed materials. 

After the seeds are well formed there is seldom any 
advantage in irrigation. Certain varieties of grain, peas 
and beans have an extended growing season, and to such 
it may be necessary to apply water some time before 
flowering, and perhaps once after seed-formation is well 
under way. Even to the crops that mature early, it may 
often be profitable to add water at the time the seeds 
are forming most rapidly, for it may help fill them more 
completely. 

116. Time of irrigating long-season crops. — Sugar 
beets, potatoes, corn and similar crops should also be 



TIME OF IRRIGATION 185 

planted in well-saturated soil. The first irrigation should 
be postponed, for the reasons already given, until the 
plants really show need of water. From the time of the 
first irrigation, water must be applied to these long- 
growing crops at regular intervals throughout the grow- 
ing season. Sugar beets, carrots, corn and like crops, 
planted usually in May, need the greater quantity of 
water in July and first half of August. From the first of 
September and during autumn, little, if any, water should 
be applied, even if the harvest does not occur until October 
or November. Sugar beets are seldom benefited by irri- 
gation after the first of September. 

Under the conditions of the inter-mountain coun- 
try and on deep clayey or loamy soils, 5 inches of water is a 
fairly large single application. An irrigation of this 
degree every two or three weeks throughout the season, 
from the time of the first irrigation until the first week in 
September, is quite sufficient to maintain the soil in a 
first-class condition for the needs of beets and other long- 
season crops. Usually, a much smaller quantity of water 
at each irrigation will suffice to produce a bountiful har- 
vest of root crops. It is doubtful, however, if more than 
three weeks should elapse between irrigations, where 
water is fairly abundant, for if the soil dries out too much 
the plant may be injured permanently. When 15 acre- 
inches are applied throughout the season it is well to 
apply them in four or five irrigations. The deeper the 
soil, and the more thorough the surface-cultivation, the 
fewer need be the applications. During the hot season, they 
will naturally be closer together than in the early or late 
summer. In one series of experiments, the highest yield 
of carrots, a long-season crop, was obtained with seven 
irrigations; the highest yield of sugar beets was obtained 



186 IRRIGATION PRACTICE 

with six irrigations. Excellent crops of carrots were, how- 
ever, obtained with four irrigations, and of sugar beets, 
with only two irrigations. Each district must work out 
the problem for itself, keeping well in mind that root 
crops must be made to wait as long as possible for the 
first irrigation and that thereafter, until early fall, they 
should receive rather regular irrigations. 

Lucern, or alfalfa, should be watered with reference 
to the number and times of cuttings. Over the irrigated 
district three cuttings of lucern are ordinarily obtained 
annually. The first irrigation should be applied when the 
crop goes into flower, which is the time of the greatest 
rate of growth. The next irrigation may be applied just 
before or after the first cutting. This second irrigation 
is intended, primarily, for the use of the second crop, and 
its chief effect is to stimulate the early growth of the 
second cutting. It matters little whether the crop be irri- 
gated immediately before or after the cutting. It is pos- 
sible that an irrigation before cutting permits the water to 
be distributed more thoroughly in the soil, before the 
growth of the second cutting begins. On the other hand, 
the longer the interval between the irrigation and the cut- 
ting of the first crop, the larger the loss by evaporation. 
Each cutting of lucern could well receive an irrigation at 
the time of flowering and another at the time of cutting, 
excepting the third crop, which is usually cut so late as 
to require no further irrigation, unless it be the fall irri- 
gation which is practised for the benefit of next crop. 

Hay crops that yield only one cutting a year should 
be treated very much as is the first cutting of lucern. 
The one irrigation should be applied at the time of flow- 
ering or seed time. If the aftermath is to be used, one or 
more small applications may be applied throughout the 



TIME OF IRRIGATION 187 

season, to maintain the late growth. Pastures which in 
the irrigated section are maintained during the whole 
season require small but regular applications of water 
from spring to fall. 

The time to apply water to fruit trees depends on 
both fruit- and bud-formation. The fruit-buds are formed 
the year preceding the bearing of the fruit. At the time 
that these are formed, usually in late midsummer, when 
the fruit is still small and immature, the crop should be 
plentifully supplied with water. Fruit trees require a 
moderate amount of water in the spring and early summer 
with an increasing quantity as the summer advances and 
the fruit develops. Late fall irrigation of orchards, after 
the season's wood has ripened, is beneficial to the succeed- 
ing crop, except in places where the winter precipitation 
is very heavy. 

117. Night vs. day irrigation. — Water is usually 
allowed to run through the canals with equal volume by 
day and by night. The night water, so far as is known, is 
quite as valuable as the day water in crop-production. 
However, night irrigation naturally is more difficult to 
perform. Sanborn and others have experimented on the 
relative value of night and day irrigation. Their results 
lead to the conclusion that there is no material difference 
in results between night and day irrigation. Where the 
water supply is small, it must be husbanded carefully, 
and the farmer then uses it both day and night. 

REFERENCES 

Harris, F. S. Studies in Soil Moisture and Fertility. 

Harris, F. S. Long versus Short Periods of Transpiration in Plants 
Used as Indicators of Soil Fertility. Proceedings of the Ameri- 
can Society of Agronomy, Vol. II, p. 93 (1910). 



188 IRRIGATION PRACTICE 

McClatchie, Alfred J. Winter Irrigation of Deciduous Orchards. 

Arizona Experiment Station, Bulletin No. 37 (1901) ; also United 

States Department of Agriculture, Farmers' Bulletin No. 144 

(1901). 
McDowell, R. H. Irrigation. Nevada Experiment Station, 

Bulletin No. 25 (1894). 
Richman, E. S. United States Horticultural Department Bulletin 

No. 20 (1893). 
Sanborn, J. W. Night versus Day Irrigation. Utah Experiment 

Station, BuUetin No. 21 (1893). 
Welch, J. S. Irrigation Practice. Idaho Experiment Station, 

Bulletin No. 74 (1914). 
Widtsoe, J. A., and Merrill, L. A. Methods for Increasing the 

Crop-Producing Power of Irrigation Water. Utah Experiment 

Station, Bulletin No. 118 (1912). 



CHAPTER X 
THE METHOfi OF IRRIGATION 

The method of irrigation determines greatly the duty 
of water and the profitableness of irrigation. The con- 
siderable labor which always attends the application of 
water to land is one of the big charges to be made against 
irrigation, and one that must be made as low as possible. 
Besides, the method of irrigation frequently affects, 
directly, the degree to which plants may use the water 
applied. 

There are only two general methods of applying irri- 
gation water; first, irrigation above ground and, second, 
irrigation below ground. Each of the two methods appears 
under several variations and possesses a special advantage. 
In practice, the method of applying water above ground 
is the only one in general use. 

118. Sub-surface irrigation. — The application of 
irrigation water from below, or sub-surface irrigation, has 
the advantage that water so applied is not subjected to 
such direct evaporation from the surface as of necessity 
accompanies surface irrigation. When water is scarce, 
it is especially of great importance to reduce such evapora- 
tion. For this purpose, sub-irrigation seems to be the 
method that should be employed. 

It should, however, be kept in mind that the suc- 
cessive wetting and drying of the top soil, which accom- 
panies surface irrigation, benefits crops and enables them 
to produce dry matter with least water, and often, this 

(189) 



190 IRRIGATION PRACTICE 

benefit overshadows the loss by evaporation. In the 
Utah work, some attention was given to the effect of irri- 
gation above ground with respect to the transpiration 
ratio. In every case, much larger quantities of water 
were evaporated when the water was applied to the sur- 
face of the soil than when applied by sub-irrigation, but a 
pound of water applied to the surface produced as much 
dry matter as when applied below the surface. It may be 
that the value of sub-irrigation has been considerably 
exaggerated because the diminution of evaporation only 
has been considered. 

Aside from these theoretical considerations, sub-irri- 
gation has not received wide acceptance, due to certain 
intrinsic difficulties, which seem insurmountable. Sub- 
irrigation implies underground water channels, opened 
at various places for the escape of water to the crop. 
These underground channels are usually pipes of iron or 
concrete or wood. Machines are on the market which, 
as they move along, open the soil to the requisite depth 
and at the same time lay a concrete pipe of the desired 
dimension. The cost of installing such a system is very 
great and adds immensely to the initial cost of irrigation. 
With the present prices of land, water and crops, it is not 
good business to install sub-irrigation systems, unless it 
be in a few favored localities where conditions of labor and 
markets are just right. 

It may be urged that such a system once installed and 
out of sight requires little further attention; whereas sur- 
face irrigations require a large annual cost for the upkeep 
of ditches and the actual spreading of water over the 
land. This advantage is, however, more apparent than 
real. Leaks are often sprung in the underground systems 
which are located with difficulty and remedied at large 



METHOD OF IRRIGATION 



191 



expense. Still worse, plant roots, always in search of 
water, are gradually directed to the openings in the under- 
ground pipes, and fill them so completely that the flow 
of water is either greatly diminished, or entirely stopped. 
For this reason every sub-irrigation system has either been 
abandoned or has been maintained only in spite of the 



AiAtrJ Ca/val 




Fig. 32. Plan of a sub-irrigated farm in Idaho. 



great cost of keeping the water outlets free from plant 
roots. The best that can be said about sub-irrigation is 
that the method has not yet been perfected, and that it 
offers a fine field for the agricultural inventor. 

One kind of sub-irrigation of extremely limited appli- 
cation has proved successful. In certain localities are 
found somewhat sandy soils, 1 to 5 feet in depth, under- 
laid by an almost impervious clay. Ditches are dug at 
intervals of Y% to % mile. The water flowing through these 



192 



IRRIGATION PRACTICE 



ditches sinks until it reaches the clay bottom, along which 
it travels for great distances within reach of plant roots. 
Some of the finest fields in western America are supplied 
with water by this inexpensive process of natural lateral 
seepage. Clearly, this method is so limited in extent that 



MAIN VALVE 
-Am vnir 




GRAVEL 

Fig. 33. Lee's sub-irrigation system. 

it deserves only a passing notice. Yet it should be kept in 
mind, so that, whenever the conditions appear to be 
suitable, attempts may be made to irrigate crops by 
natural sub-irrigation. (Figs. 32, 33.) 

Except in greenhouses and under natural systems, sub- 
irrigation may be eliminated from consideration. 



METHOD OF IRRIGATION 193 

119. Surface irrigation. — Surface irrigation is the 
method generally adopted in all irrigated countries. 
There is a great variety of methods of surface irrigation, 
most of which are scarcely worth consideration, because 
they either fail to recognize the natural laws underlying 
irrigation, or their cost of installation is beyond practi- 
cability. 

The approved methods of surface irrigation may be 
classified under two heads: first, the flooding method; 
second, the furrowing method. By the flooding method, 
all the soil is covered by the water applied; by the furrow- 
ing method, the water is guided in furrows or channels 
which traverse the whole field, but the water covers only 
a part of the soil surface. Both flooding and furrowing 
are used extensively in all irrigated regions. In one 
locality flooding may be the general method; in another, 
furrowing. The adoption of one or the other of these 
methods depends sometimes upon careful trials, but more 
often upon custom following the first practices. 

The chief factors determining the choice between flood- 
ing and furrowing, are: (1) the nature of the soil, (2) the 
contour of the land, (3) the head of the water stream, 
(4) the quantity of water available, and (5) the nature of 
the crop. 

If the soil is light and "washes" — a condition exist- 
ing over large areas of the irrigated section — furrowing 
is the only really practicable method. On such soils, the 
soil-washing due to flooding often results in large chan- 
nels, gullies or "washes" being cut in the soil. On heavier 
soils, flooding may be practised safely, as far as erosion is 
concerned. Many soils, after having been wetted, bake and 
form a hard crust, which is injurious to the soil and to 
the plant. On such soils the furrowing method is advisa- 

M 



194 IRRIGATION PRACTICE 

ble, for by that method only a part of the surface is cov- 
ered with water, and that part may be covered with loose 
earth by cultivation soon after irrigation. Other soils, 
after having been wetted, as they dry, fall apart, form- 
ing natural mulches. On these soils, flooding is quite 
safe. 

On relatively level land, either flooding or furrowing 
may be adopted. Flooding is best done when the slope of 
the land is not great, especially if the soil tends to "wash" 
easily. On steeper lands, furrowing must be employed. 
The heavier the soil, the steeper may be the inclination; 
the lighter the soil, the gentler must be the inclination. 
On the relatively steep slopes, frequently used for orchards, 
furrowing, alone, is employed, and the sharp descents are 
overcome by carrying the furrows back and forth around 
the slopes with any desired fall. While no definite rule 
can be laid down as to the permissible inclination of 
lands under irrigation, yet a farmer soon learns by experi- 
ence the practice best suited to his land. Farm irriga- 
tion systems should be laid out with reference to the con- 
tour of the land and, therefore, the irrigation farmer 
should first secure contour maps of the land which he in- 
tends to bring under irrigation. 

By the "head" is understood the volume of water 
supplied to the unit of time. Under some systems of canal 
management, farmers are given large streams of water 
for short times; under other systems, small streams are 
available for longer periods. The total quantity of water, 
at the end of the period, may in either case be practically 
the same. A high head of water pushes rapidly over the 
land. Loose, sandy soils that absorb water rapidly must 
be irrigated with a high head of water, especially under 
the flooding method, or the water may all be drawn into 



METHOD OF IRRIGATION 195 

the soil, before the lower end of the field is reached. Under 
the flooding method, a high head of water may be used on 
nearly all soils, but a low head is suitable only for heavier 
soils. It follows that the furrowing method is best adapted 
where the head of water is low; the flooding method where 
the head is high. This deduction has found practical 
expression over the whole irrigated area. 

If irrigation water is abundant, and a high head may 
consequently be secured, the flooding method is usually 
employed. If water is scarce, the main consideration is 
to make the total supply cover the largest number of 
acres, and the furrowing method is ordinarily employed, 
since by this method a small quantity of water may be 
made to cover much land. It has been shown that the 
productive power of water decreases as the total quantity 
applied to a given area is increased. That is, with each 
additional inch of water, less dry matter is produced. 
Consequently, where water is scarce, it is more profitable 
to spread the small quantity of water over a large area of 
land. To do this, the furrow method is indispensable. In 
irrigation practice, therefore, although the reason is not 
always understood, the furrowing method is invariably 
used wherever the supply of water is low. 

The nature of the crop determines, also, the method of 
irrigation. Some plants are more sensitive than others to 
contact with water. It is believed by many that the 
sugar beet is injured whenever irrigation water is allowed 
to come into contact with it, especially if the day is hot. 
This may be true at times, but this danger is much exag- 
gerated. Only when water stands against a plant for 
some time is injury really likely, and, then, injury comes 
either when the water is so hot as to cause sun-scald 
or so cold as to chill the plant. In either case, the process 



196 



IRRIGATION PRACTICE 



of growth is retarded. Much work yet needs to be done 
on this subject. 

The various modifications of the flooding method 
may be grouped into (1) flooding open fields, and (2) flood- 
ing closed fields. Open fields are those not surrounded by 
levees. Closed fields are those completely surrounded by 
levees, making a compartment into which water is 
admitted. 

120. Permanent ditches. — A permanent system of 
ditches, having in view immediate and probably future 




Fig. 34. A permanent ditch in an orange grove (Redlands). 

needs, should be constructed on every farm, to connect 
the canal with the field to be irrigated. The ditches should 
be placed so as to interfere as little as possible with regu- 
lar agricultural operations, and they should conform 
either to the contour of the land, or to some well defined 
plan for dividing the farm into fields. The laying out and 



METHOD OF IRRIGATION 



197 



construction of permanent ditches is the first big thing in 
irrigation agriculture. Great waste has occurred and is 
occurring because of carelessness in this matter. 

The ditches, once decided upon, should be built in a 
permanent fashion, so that they will not need to be 



T 



F/ETLD LATERAL 



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i' 'ri'l i ill ' •• 

liiiiiiiiililWiii'lii.. 



^H£AD\D/TCH 



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.......J-"""" I 



■•■"I 

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....-•I 



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lit 



itt 



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lilliilfiiliilllliillilll 



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| ^W/fS7£\D/TC// 1, 



y 



Fig. 35. Plan of field-ditch irrigation. 

repaired greatly from year to year. In the older and more 
prosperous irrigated sections, ditches are often made of 
concrete and are ' consequently practically indestructible. 
The best illustration of this kind of ditch is found in Cali- 
fornia, notably in the Riverside district, where the orange 
groves require that water be made to do its highest duty. 



198 



IRRIGATION PRACTICE 




Fig. 36. Flooding from ditches running down the steepest slope. 

The main permanent ditches if made of concrete, are fre- 
quently put underground, out of sight and out of the way. 
The water is allowed to escape through stand-pipes into 
the temporary ditches of the farm. The beauty and often 
the prosperity of the irrigated farm depend upon the 
permanent ditches. (Fig. 34.) 

121. Field-ditch or field-lateral method. — This method, 







Fig. 37. Flooding from field ditch. 



METHOD OF IRRIGATION 199 

which is the most largely used method of open field-flood- 
ing, is especially adapted to level lands with gentle slopes. 
By this method, the water is taken out of the main ditches 
at various intervals, and as it flows over the field, is dis- 
tributed properly over the field by small temporary 
ditches or furrows. These small laterals follow the high 




Fig. 38. Flooding with aid of canvas dam. 

places of the field, and the water overflowing their banks 
covers the field. 

For instance, wheat is planted in the usual way, with- 
out reference to the field ditches which are made after 
the wheat has germinated and is a few inches high. The 
small laterals are made with a small horse-plow made for 
the purpose, or they are made by the irrigator with a hoe. 
The field ditches of lucern and similar permanent crops, 
once made, remain from year to year, except that they 
may be deepened a little from season to season. These 



200 



IRRIGATION PRACTICE 




Fig. 39. Laterals made in field and dammed with small piles of manure for 

next year's irrigation. 

field ditches, however, whether in wheat or alfalfa, are 
so small as to be of no hindrance in the cultural operations 
of the farm. 

The essential feature of this method of irrigation is 
the guiding of the water over the land through numberless 
furrows or small ditches. This is hard and slow work. 
One man can cover daily only a few acres at most by this 
method. The greatest advantage of the field-ditch method 



METHOD OF IRRIGATION 



201 



is that the first cost of preparing the land for irrigation is 
small; the top soil is not disturbed, and the field is not 
cut up by levees that make ordinary farming operations 
difficult. The disadvantages are that the necessary 
field labor is hard; the field ditches must be made over 
from year to year; and, finally, it is difficult to secure 
an even distribution. It is clear, however, from the 
great extension of this method that the advantages over- 
shadow the disadvantages. This is the method employed 
by the Mormon pioneers when they founded irrigation 
in the Salt Lake Valley and is still one of the safest methods 
of irrigation in Utah, Idaho, Wyoming, Colorado and some 
of the other irrigated states. Practically all manner of 
crops, except those planted and cultivated in rows, can 
be irrigated by this method. In spite of its disadvantages, 
immense yields, the largest on record, have been secured 
by this method of irrigation. (Figs. 35-39.) 



Dike 



Dike 



r 



Fig. 40. Plan for border irrigation. 



202 



IRRIGATION PRACTICE 




Fig. 41. Border method of irrigation. 



122. The border method. — The border method of 
irrigation is an open-field method. By this method the 
field is divided by low flat ridges of earth into long narrow- 
strips, the lower ends of which are open. The ridges are 
spaced about 50 feet apart and are frequently 800 feet 
long. Water is guided over the land by field ditches. This 
modification of the field-ditch method has for its purpose 
the better control of the water. The ridges prevent the 
water from spreading beyond the distance determined 

between the ridges. 
This enables the 
irrigator to watch the 
water more closely. 
When the water 
reaches the lower end 
of the strip, it may be 
shut off and another 
strip attacked. The advantages and disadvantages are, 
practically, those explained for the field-ditch method, 
except that the lateral ridges make the handling of the 
water somewhat easier. In cultural operations the ridges 
are in the way. (Figs. 40, 41.) 

123. The check method. — This is the most important 
of the closed -field variation of applying water by the 
flooding method. The field is laid off into compartments 
or checks wholly surrounded by levees. The water is 
admitted at the upper end and completely fills the com- 
partments until, in many cases, it overflows at the lowest 
point of the levee. This method of irrigation has been 
practised from the earliest antiquity. The irrigated 
countries of Europe, Asia and Africa employ this method 
very largely. 

Evidently it is adapted only to comparatively level 



204 



IRRIGATION PRACTICE 



land; if the slope is great, the lower levee must be made 
too high for practical purposes. A large head is always 
necessary; for, if the head is small, the land, especially if 
sandy, is likely to absorb the water so fast at the upper 




Fig. 43. Rectangular check method of irrigation. 



end that the lower end receives only a small part of the 
water intended to cover the whole check. The flow of 
water should be from 5 to 10 second-feet in order to make 
the method thoroughly successful. In the older countries, 
the checks are usually small. In America, the checks are 
often very large — from 10 to 20 or more acres. The 
check method of irrigation, to be really successful, must 
be practised with small checks, at the most from 1 to 3 
acres in area. 

The compartments may be laid off in various ways. 
If the land does not slope too much, the whole farm is 
laid off into square or rectangular checks, into which the 
water is admitted in succession. Where the land is uneven, 
or the slope steep, the checks are made to conform to 
the contour of the land. In either case, water must be 
admitted at the highest point and be brought rapidly into 
the compartment so that the ground may be covered 
thoroughly and in a short time. At times a depression is 



METHOD OF IRRIGATION 



205 



made in the lower levee over which the excess of water 
passes into the next lower check. 

The check method of irrigation has some advantages. 
Once the checks or the levees have been well constructed, 
one man may irrigate 7 to 15 acres a day. The cost of 
preparing the land for irrigation, after the first year, 
when the levees are made, is very small. The quantity 
of water applied can be very accurately gauged and 
evenly distributed by this method. For crops such as rice, 
which demand that the soil be kept moist or even sub- 
merged for long periods throughout the year, the check 
method of irrigation is indispensable. Such crops are few, 
and the check method is, in fact, used more extensively 




Haj.i& ntvacr- 



Fig. 44. Contour check method of irrigation. 

for other crops. The check method of irrigation also has 
many disadvantages. The levees cost from $7 to $20 an 
acre, under American conditions, where the compartments 
are large. The cultural operations of the farm are delayed 
and the machinery damaged by passing back and forth 
over the high levees. In any case, they are in the way 



206 



IRRIGATION PRACTICE 



and are a disagreeable feature on the farm. The farmer 
finds it difficult to change to new and possibly better 
cropping systems, without going to the large expense of 
leveling the old levees and throwing up new ones. If 
the soil bakes, this method should not be employed at all, 
since water covers, for some time, the whole area. It is 
impossible by this method to keep water from touching 




Fig. 45. Filling checks with detachable pipes. 

the crop. The relatively large quantities of water that 
must be used by this method tend to keep the roots very 
near the surface, and the crop will be more intensely 
affected by adverse conditions of heat or cold. 

The check method is, next to the field-ditch method, 
the most important method of applying water to crops; 
yet, its disadvantages overshadow its advantages, and it 
is a method which, in all probability, will gradually pass 



METHOD OF IRRIGATION 



207 



out of general use, and be retained only where crop, soil 
or other conditions make it necessary. (Figs. 42-45.) 

124. The basin method. — The basin method is prac- 
tically identical 
with the check 
method. It re- 
fers to checks in 
orchards with a 
tree in the cen- 
ter of each, and 
with temporary 
levees. Earth is 
heaped around 
the tree trunks 
to keep the water 
away from the 
bark. This method is used especially in mild climates 
where fall or winter irrigation is practised. The use of 
this method is also rapidly decreasing, and is likely soon 
to pass out of practice. The advantages and disadvan- 
tages of this method of irrigation are those discussed 
under the check method. (Figs. 46-48.) 

125. The furrow 




Fig. 46. Orchard irrigation by basin method. 



a&"£a&4i*^i ■&&■&&$ 




Fig. 47. Orchard irrigation by basin method. 



method. — In this 
method of irrigation, 
small furrows leading 
from the supply ditch 
traverse the fields to 
be irrigated. Water 
flows down the fur- 
rows and is absorbed 
by the soil. Next to 
the method of flood- 



208 



IRRIGATION PRACTICE 



ing by field ditches, this is the most common method of 
irrigation, and it promises, at least in America, to super- 
sede all other methods. 
(Figs. 49, 50.) 

After the crop has 
been planted, small 
furrows leading from 
the supply ditch at 
the head of the field are made to cover the field by 
some of the many kinds of markers or furrowers. This 
process of furrowing the land is known as "marking" or 




Fig. 48. Grading of interior of basins to pre- 
vent water from coming in contact with 
trees. 




Fig. 49. Furrow irrigation. 



METHOD OF IRRIGATION 



209 



"laying off" the land. (Fig. 52.) The furrows are made at 
right angles to the supply ditch, or, if the land is irregular 
in contour, they are made to follow the contour lines. 
This is done, especially, in orchards where trees grow 




Fig. 50. Furrow irrigation of young alfalfa. 

on the hillsides. It is not an uncommon sight in such 
districts to see thirty or forty furrows filled with water 
zigzagging down a hillside. 

The furrows are made from year to year, except in the 
case of alfalfa and other perennial crops. Alfalfa, when 
irrigated by this method, is furrowed the first year, and 
the permanent furrows are only deepened or cleaned out 
from year to year. The disadvantage of the permanent 
furrows is that as the mower travels across them the rider 
is shaken up considerably and the machine is injured. In 
wheat fields, furrows are laid off soon after the wheat is 
planted, when it is about 3 or 4 inches high. Fields of 
sugar beets, potatoes and similar crops are furrowed just 
before the first irrigation. One furrow is ordinarily made 
between every two rows of plants, although on some soils 

N 



210 



IRRIGATION PRACTICE 



the distance between furrows is greater. In orchards, the 
furrows are usually made at the time of the first irrigation. 
When the trees are young, one furrow is made on each 
side of each row, perhaps 2 feet or a little more away from 
the tree. As the tree becomes older and the root-system 



'Turnout Stone? 



iKj (-/urrroup o i anu r m , 



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v*3 







m m 




m m m 



Overf/ow 
■St ana" • 



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71 






Overf/ow 
Stone/* 



Fig. 51. One-way furrow irrigation. 



expands, the furrow is moved away from the tree until, as 
the tree approaches maturity and more water is needed, 
three or four furrows may be made between two rows of 
trees. The principle in spacing the furrows is that the 
furrows shall be so close together that the water soaking 
from the furrows into the soil will meet and thoroughly 



METHOD OF IRRIGATION 



211 



saturate the soil below the surface. In orchards where 
trees are 16 to 20 feet apart, one furrow cannot do this 
and several furrows are employed. The reason for using 
only one furrow when the tree is young is that the roots 
have not spread sufficiently to make use of water that 
might be applied half way between the rows of trees; and, 
moreover, the young tree needs little water. Fewer and 




Fig. 52. Furrowing land. 

deeper furrows are now generally used in the irrigation 
of orchards and other crops. Fortier and others have 
shown that the deep furrow has a decided advantage 
over the shallow furrow. (Figs. 51, 53-55.) 

The furrow method is in many ways an ideal method 
of irrigation. It enables the farmer to control the quantity 
of water added to a soil. It makes it possible to spread a 
small quantity of water over a relatively large area of 
land. It prevents the washing and consequent destruc- 



212 



IRRIGATION PRACTICE 



tion of the light soils characteristic of arid regions. It 
reduces evaporation; tends to prevent over-irrigation, 
and, because of the ease with which the furrow may be 
covered, soon after irrigation, the rise of alkali is delayed. 
There is little disturbance of the top soil, and baking is 




.^^mmmmsmMmm 



Fig. 53. Standpipe supplying furrows with water. 

largely eliminated. The system once laid off requires 
little attention; one man can irrigate a large number of 
acres in one day. The method is inexpensive. 

The furrow method of irrigation also has some dis- 
advantages. Large heads of water cannot be used in the 
small furrows. It may be desirable, especially in the 
spring, to apply quickly a large quantity of water to a 
given field. This is practically impossible with the fur- 
row method of irrigation. It is difficult to admit the 
same quantity of water to each of the many furrows. 
Special attention must, therefore, be given to establishing 
checks in the supply ditch at suitable intervals, to force, 
as nearly as may be, the same quantity of water into each 
furrow. Tubes or lath boxes, connecting the furrows with 
the supply ditch, are helpful in establishing a steady flow 
in each furrow. (Fig. 56.) The uniform use of water 



METHOD OF IRRIGATION 



213 



throughout the length of the furrow is very difficult. On 
sandy soils, especially, the upper end of the furrow 
absorbs so much water that little is left for the lower end. 
In fact, when the furrow is long, it frequently happens 
that the water disappears before the lower end is reached. 
The best way to overcome this difficulty is probably to 
shorten the furrows, and to have a series of temporary 
supply ditches for each series of furrows. 

Finally, the soil is benefited by being occasionally 
covered with water. The Utah work showed that, with 
a given quantity of water, as large yields were invariably 
obtained when the water was applied by flooding as by 
furrowing, in spite of the greater loss by evaporation 



eilKC/tr^ATt 




Fig. 54. Zigzag furrows to insure uniform distribution over soiL 



214 



IRRIGATION PRACTICE 




Fig. 55. Another type of zigzag furrows. 



under the flooding method. It may be well, therefore, to 
allow the water to overflow occasionally even under the 

furrow method of 
irrigation. The same 
effect may be ob- 
tained in part by 
placing the furrows 
differently from year 
to year. Meanwhile, 
the furrow method, 
with a given quantity 
of water, will yield as heavily as will the flooding method, 
and may yield more. 

126. Summary. — In brief, there are, in practice, only 
two great methods of irrigation: (1) flooding by field 
ditches, and (2) furrowing. The field-ditch method is in 
reality a furrowing method, in which the water overflows 
the banks of the fur- 
rows. On certain soils 
and under certain 
conditions the field- 
ditch method will be 
found most service- 
able; on others, the 
furrowing method. 
The closed field 

methods are likely to vanish quite rapidly because of 
the large expense of installation and the want of elastic- 
ity in the system. The method of irrigation by furrows 
will probably triumph as the great method of applying 
water to soils for the production of crops. At the present 
time the field-ditch and the furrowing methods are in 
chief use. 




Fig. 56. Lath-box for distributing water to 
furrows from head ditch. 



METHOD OF IRRIGATION 215 



REFERENCES 

Fortier, Samuel. Methods of Applying Water to Crops. United 
States Department of Agriculture, Yearbook for 1909, p. 293. 

Fortier, Samuel, and Beckett, S. H. Evaporation from Irrigated 
Soils. United States Department of Agriculture, Office of 
Experiment Stations, Bulletin No. 248 (1912). 

Loughridge, R. H. Distribution of Water in the Soil in Furrow 
Irrigation. United States Department of Agriculture, Office 
of Experiment Stations, Bulletin No. 203 (1908). 

Mead, Elwood, et al. Preparing Land for Irrigation and Methods 
of Applying Water. United States Department of Agriculture, 
Office of Experiment Stations, Bulletin No. 145 (1904). 

Wickson, E. J. Irrigation Among Fruit-Growers on the Pacific 
Coast. United States Department of Agriculture, Office of 
Experiment Stations, Bulletin No. 108 (1902). 

Widtsoe, J. A. Factors Influencing Evaporation and Transpira- 
tion. Utah Experiment Station, Bulletin No. 105 (1909). 

Widtsoe, J. A., and Merrill, L. A. Methods for Increasing the 
Crop-Producing Power of Irrigation Water. Utah Experi- 
ment Station, Bulletin No. 116 (1912). 



CHAPTER XI 
CROP COMPOSITION 

Crops have been valued almost entirely by weight. A 
bushel of wheat has been a bushel of wheat, providing it 
weighed sixty pounds. Of late years it has been determined 
that the quality may be as important as the quantity 
in determining the value of a crop as a food for man or 
beast. The time is undoubtedly near when crops will be 
judged in the markets by quality as well as by quantity. 

Many agricultural industries already make significant 
use of quality valuation. Sugar-beet factories purchase 
beets at a given price a ton, but the price is conditioned 
on the sugar content, and the contracts with the farmers 
always specify a minimum percentage of sugar. Potatoes, 
when made into starch are valued on the basis of starch 
content. Grains are graded by quality. Fruits are classed 
according to color, size and other characteristics. Many 
other crops are likewise valued according to composition 
as well as to actual weight. 

As knowledge concerning food and its relation to the 
animal body becomes popularized, there will be an increas- 
ing demand for foods of definite composition which will 
affect the world markets until a scale of prices based on 
weight and composition shall be established for each crop. 
In that day, the irrigation farmer will have a great advan- 
tage, for the regular variation of plant composition with 
the quantity of water applied makes it possible under 
the controlled water supply of irrigation to regulate in a 

(216) 



CROP COMPOSITION 217 

measure the quality of the crops produced. Irrigation, or 
the artificial application of water to crops, requires added 
labor. It is, therefore, only upon the basis of certain 
and larger yields, and better quality of the crops produced, 
that irrigated areas may compete in the open markets 
with other sections of the world. 

The relation between irrigation and crop composi- 
tion has been studied by several investigators. In general, 
it has been shown that many irrigated crops may be 
made to possess a composition superior to that of crops 
grown under the natural rainfall. Yet, it must be admit- 
ted that we know the merest outlines of the subject. 
There is here a great and important field open for investi- 
gation by those who are interested in developing a science 
of irrigation 

127. Groups of plant constituents. — Every plant con- 
tains five great groups of substances and each has a defi- 
nite food value and bears important relationships to the 
soil on which the plant has been grown. These are: (1) 
water, (2) ash or mineral matter, (3) nitrogenous sub- 
stances, (4) fats, and (5) carbohydrates. 

128. Water. — During the life of the plant, large quan- 
tities of water are passed rapidly from the soil into the 
plant, and from the plant leaves into the air. As has been 
shown, hundreds of pounds of water are thus passed 
through the plant for the production of one pound of dry 
matter. That the vital processes of the plant may pro- 
ceed unhindered, the cells of the green plant must be fully 
filled with water. The more water is in the soil, the more 
completely are the plant cells filled with water. That is, 
on a moist soil, under conditions of abundant irrigation, 
the green plant probably contains a larger proportion of 
water than on dry soils, where the quantity of irrigation 



218 IRRIGATION PRACTICE 

water applied is small. This effect is felt most in the 
stalks of plants. In the leaves, which naturally contain 
less water than do the stalks, the effect of varying quan- 
tities of water is not so apparent; but the water content 
of every part of the plant is somewhat affected by the 
water supply. The underground parts of plants, such as 
potatoes and sugar beets, contain usually a slightly 
larger percentage of moisture, when grown on land 
abundantly irrigated. 

Since most crops are not sold green, this effect of irri- 
gation has little commercial value. True, in the case of 
fruits, tomatoes and similar crops, which are usually dis- 
posed of in an undried condition, the increased percent- 
age of water in crops grown with much water may make 
considerable difference in the final weight. Potatoes and 
sugar beets, when irrigated heavily and late, may weigh 
more per acre, but the increased yield is obtained only at 
the sacrifice of quality. In most cases the difference is 
so small as to be negligible. 

The water content of hay, grain and other crops that 
are sold after thorough curing or ripening, is not influenced 
by the irrigation during growth. However, hay, cured 
under the dry conditions of the arid region, contains less 
water and is to that extent more valuable than hay cured 
in the humid regions. Likewise, the water content of 
wheat and similar crops that ripen before harvesting is 
only slightly influenced by the degree of irrigation; but 
the dry conditions of the arid region tend to yield crops 
containing less water than when grown under humid 
conditions. In short, irrigated crops of the arid region, 
that are dried before being placed on the market, are more 
valuable, pound for pound, than those grown in humid 
regions, for the reason that under humid conditions the 



CROP COMPOSITION 



219 



drying-out cannot be so complete. Stewart has shown 
that this difference may have very noticeable financial 
results when large shipments of grain are made from the 
arid regions. 

129. Ash. — The ash, or incombustible portion of 
plants, represents, roughly, the food taken from the soil 
by the plant. It is, therefore, important in considering 
the maintenance of soil fertility. The effect of much or 
little soil moisture upon the quantity of ash taken up 
by the plant has been investigated by many students. In 
general, the percentage of ash in the dry substance be- 
comes larger as the quantity of irrigation water or the 
soil moisture increases. The following table shows some 
typical results under irrigated conditions : 



Degree of 
irrigation 


Percentage of ash in dry matter of 


Oat 
leaves 


Oat 

stalks 


Oat 
heads 


Sugar 
beets 


Potato 
tubers 


Medium .... 
Small 


21.10 
19.57 
17.13 


8.68 

7.72 
7.27 


6.38 
6.03 
5.29 


6.15 
6.02 
6.18 


3.36 

3.89 
4.39 



As the supply of water increases, there is usually a 
very marked increase in the percentage of ash in the 
leaves, a smaller increase in the stalks, and a yet smaller 
increase in the underground parts of the plant. This 
relative variation among the plant parts seems to be a 
general rule, although observations are on record show- 
ing a decrease in the percentage of ash in the under- 
ground parts as the irrigations are made larger. 

Tollens and others have shown that, in general, this 
law of increase is true for each ash constituent as for the 
total ash. Lime is taken up very abundantly by the plant 



220 IRRIGATION PRACTICE 

as the supply of water increases; and potassium, phos- 
phorus, and other important plant-foods are likewise 
taken up in larger proportion to the dry matter as the 
supply of water is increased. 

This law, that the percentage of ash in plants increases 
as the irrigation water is increased, means, apparently, 
that more plant-food is used to produce a unit of dry 
matter as more water is used in irrigation. This is one of 
the strongest arguments yet found against the excessive 
use of water. The farmer who uses a small quantity of 
water in crop-production not only obtains a larger amount 
of dry matter for each unit of water used, but also uses a 
smaller quantity of plant-food for each unit of dry matter. 
The waste due to over-irrigation is, therefore, at least 
twofold: it diminishes the yield of dry matter to the unit 
of water used, and it increases the soil-fertility cost per unit 
of dry matter. This must be a fundamental considera- 
tion in the establishment of a permanent system of agri- 
culture under irrigation. 

130. Protein. — Protein is the term commonly applied 
to all organic plant substances containing nitrogen. These 
nitrogenous plant constituents are of greatest impor- 
tance in the maintenance of animal life. When organized 
into proteid forms, they form the basis of blood, muscles 
and all other primary tissues of the animal body. In fact, 
as a food for animals, the value of a crop may be well 
measured by its percentage of nitrogenous substances. 
The compounds containing nitrogen are not, however, 
all of equal value. Some furnish merely body heat, while 
others enter into the fundamental structures of the body. 
In the investigations of the effect of irrigation on plant 
composition, attention has been given mainly to the group 
of substances under the name "protein, " and little knowl- 



CROP COMPOSITION 



221 



edge exists concerning the variations of the individual 
compounds occurring under this general head. 

The percentage of protein in plants is very sensitive to 
irrigation. The more water used, the smaller is the per- 
centage of protein in the resulting plant. This is almost 
invariably true. In the following table is given the per- 
centage of protein in several crops, when small, medium 
or large quantities of water were used in the production 
of the crop. 

Percentage of Protein in Dry Matter with Varying Degrees 

of Irrigation 



Crop 



Degree of irrigation 



Small 



Medium 



Large 



Wheat kernels. Shallow soil 
"Wheat kernels. Deep soil . 

Oat leaves 

Oat stalks 

Oat kernels 

Pea kernels 

Sugar beets (roots) .... 
Sugar beets (leaves) . . . 
Potatoes (tubers) .... 

Potatoes (leaves) 

Corn kernels 

Alfalfa. Third crop . . . 

Apples, Gano 

Apples, Jonathan .... 

Pears, Bartlett 

Blackberries 

Grapes 

Raspberries 

Strawberries 

Peaches, Elberta 

Plums, Green Gage .... 
Cherries, Bing 



Per cent 

26.72 

18.05 

8.88 

3.50 

19.74 

26.08 

9.83 

15.42 

12.24 

15.43 

15.08 

17.94 

1.67 

1.43 

2.87 

7.76 

8.36 

8.14 

6.52 

4.21 

4.34 

5.57 



Per cent 
23.02 
16.45 
7.11 
3.17 
18.65 
23.32 



10.91 
13.81 
13.17 
17.44 



Per cent 

15.26 

15.98 

5.86 

2.72 

17.81 

21.96 

5.16 

14.16 

9.49 

12.69 

12.05 

16.50 

0.94 

1.17 

1.26 

5.66 

4.33 

5.19 

6.42 

3.87 

2.42 

4.48 



Every crop in the table, even apples, pears and small 
fruits, shows a diminishing percentage of protein with 
an increasing volume of irrigation water. The law is 



222 IRRIGATION PRACTICE 

undoubtedly of very wide application. In the above 
table, the percentage of protein in plant parts is also given. 
In general, the percentage of protein is diminished in 
every part of the plant when the irrigation is increased. 
The little existing knowledge indicates that the proteid 
parts of protein, used in the production of blood and 
muscle, are affected by varying irrigations, even more 
strongly than is the protein, and in the same direction. 
Some little work has also been done upon protein digesti- 
bility as affected by irrigation; and it seems safe to assert 
that when crops are grown with increasing quantities of 
water there is a decreasing percentage of digestible, 
nitrogenous substances in the plant. It is clear, there- 
fore, that plants and plant parts are more valuable as 
animal foods, pound for pound, when grown with little 
water. 

The quantity of nitrogen taken up by a crop is not, 
however, largely affected by irrigation. Whether the crop 
has received much or little irrigation water during the 
period of growth, the total quantity of protein that it 
contains per acre is approximately the same. For most 
crops the tendency is for the total yield of protein to 
increase with much irrigation, though the percentage 
decreases. 

The compounds of nitrogen from which protein is 
made, are taken, as is the ash previously discussed, by 
the roots from the soil. It would be expected, therefore, 
that the protein should vary as does the ash content. 
Instead, the variation is the opposite. Nitrogen is pres- 
ent in the soil in relatively small amounts, and, in its 
soluble and available forms, in even smaller amounts. 
Nitrification and similar processes which convert the 
organic nitrogen into forms available to plants go on at 



CROP COMPOSITION 223 

a slow rate. In the spring and early summer when the 
demand of the young plant for protoplasmic material is 
greatest, the relatively small quantities of available 
nitrogen in the soil, accumulated since the last harvest, 
are eagerly and quickly absorbed. From then on, the 
small supply of nitrogen is that made available by nitrifi- 
cation and similar processes. Moreover, after the proto- 
plasmic materials have once been made, it is doubtful if 
the plant's demand for nitrogen continues unabated. 

The protein in the plant is thus obtained in the early 
stages of growth. Carbon assimilation, however, con- 
tinues until the period of ripening, and the more water 
used the more dry matter produced. In any case, after 
the first periods of growth, dry matter is formed more 
rapidly than protein. Consequently, the percentage of 
protein in the dry matter decreases as the plant grows 
older and as more water is used. This seems to be the 
simplest explanation of the important law that the larger 
the irrigation, the smaller the percentage of protein in the 
dry matter produced by plants. 

Whatever explanation may be found for this law, the 
fact remains that the decreasing percentage of protein 
with increasing irrigation is another strong argument in 
favor of the use of little water in the production of crops 
under irrigation. 

131. Fat. — The quantity of fat in plants, except in 
the few crops especially grown for their fat content, is 
so small as to be of little consequence. Little is known of 
the effect of irrigation on the content of fat in plants. 
The more water used in irrigation, the larger, usually, the 
percentage of fat in the plant. This, however, is subject 
to revision as more knowledge concerning the matter is 
obtained. 



224 IRRIGATION PRACTICE 

132. Carbohydrates. — The substances included in this 
group are used in the animal body for the production of 
heat and the formation of fat. The carbohydrates are 
very important foods; but, since they are quite abun- 
dant, they are of less value than the protein. The elements 
constituting the carbohydrates are drawn from the water 
of the soil and the carbon dioxide of the air, both of which 
are more easily supplied than the ash or the nitrogen, 
the essential element in protein. For agricultural pur- 
poses it is necessary to consider under the head of carbo- 
hydrates the sugars, starches, and the woody substances 
or crude fiber. It has been well established that the per- 
centage of total carbohydrates in a plant increases as the 
quantity of irrigation water increases. That is, the per- 
centage of the sum of all the carbohydrates varies in the 
opposite direction from protein, as the quantity of irriga- 
tion water is varied. 

133. Sugars. — The sugars are many. The best known 
is beet or cane sugar. As a general though not an invariable 
rule, the percentage of sugar in a crop decreases as irriga- 
tion water increases. In the following table are presented 
a number of data secured by Jones and Palmer, in a study 
of fruits grown in Idaho. In the one column is the com- 
position of irrigated, in the other of non-irrigated fruits. 
The locality in which these fruits grew receives a rather 
large rainfall, and the conditions are not those prevailing 
under true arid conditions. The non-irrigated crops may, 
therefore, really be compared to those that have received a 
small irrigation, and the irrigated crops to those that have 
received a heavy irrigation: 



CROP COMPOSITION 



225 



Percentage of Total Sugar and Acids in Dry Matter 













Total sugar 


Acids (as HjSO^) 


Crop 


Irrigated 


Non- 
irrigated 


Irrigated 


Non- 
irrigated 


Cherries, Bing . 
Peaches, Crawforc 
Plums, Green Gaj 
Prunes, Italian 
Apples, Gano . 
Apples, Jonathan 
Blackberries 
Dewberries . . 
Grapes, Delaware 
Loganberries . 
Strawberries 


1 








49.10 
59.91 
48.20 
37.28 
63.55 
64.05 
43.72 
37.37 
45.41 
38.89 
42.69 


53.08 
65.12 
35.17 
48.31 
61.70 
63.25 
23.85 
34.52 
43.26 
30.22 
36.35 


3.48 
3.63 
4.05 
4.12 
1.97 
2.30 
3.22 
3.05 
2.79 
8.19 
5.88 


2.55 
3.90 
7.05 
3.63 
1.50 
2.32 
5.28 
7.18 
3.16 
13.47 
4.95 



Cherries, peaches, and prunes contained most sugar 
and least acids when receiving small irrigations. That is, 
these fruits became more sour as more water was used, 
On the other hand, plums, apples, grapes, loganberries 
and strawberries became sweeter as the irrigation water 
was increased. Much work is yet to be done before we 
shall know the full truth regarding this matter. Mean- 
while, from practical experience it is safe to predict that 
it will be found that the moderate irrigation of fruit 
orchards will produce the sweetest fruit. 

Investigations have been made, also, on the effect of 
irrigation on the percentage of sugar in sugar beets. Up 
to a certain low limit the percentage of sugar increases 
as irrigation increases. When excessively large quanti- 
ties of water are used, there may be a decided increase in 
sugar. With small and medium applications the differ- 
ences in the percentages of sugar are relatively small. 
This is shown in the following table, which contains 
average results of many years' experimentation by the 
Utah Station: 



o 



226 



IRRIGATION PRACTICE 



Inches of irrigation 
water applied 


Per cent sugar 
in juice 


Per cent purity 
in juice 


10 
20 
35 


15.33 
15.13 
15.41 


80.46 
81.09 
79.54 



When the water used was increased from 10 to 35 
inches, there was increase of less than one-tenth of 1 per 
cent of sugar and a difference of only about 1 per cent 
in the purity of the juice. Moderate irrigations are 
undoubtedly quite as satisfactory as larger ones in pro- 
ducing beets with a high percentage of sugar. Potatoes 
and other crops yielding much sugar, contain the highest 
percentages of sugar when medium quantities of water 
are used. In general, sweeter crops are produced by 
moderate than by either very small or very large irriga- 
tions. 

134. Starch. — Starch, one of the important foods of 
man, is found generally in plants. In potatoes, sugar 
beets and similar crops it is a chief constituent. In the 
dry matter of sugar beets the percentage of starch increases 
very rapidly with the increase in irrigation. That is, where 
large quantities of water are applied to sugar beets, much 
of the sugar is rapidly converted into starch. This is 
another argument against the use of large quantities of 
water in irrigation. In the dry matter of potatoes, grown 
largely for starch, the percentage of increase in starch, 
due to increasing irrigation, is much slower. In general, 
the starch content increases as irrigation increases. 

135. Woodiness. — The woody material or crude fiber 
of plants, made up largely of cellulose, is of little value 
as a food. It is influenced very strongly by irrigation 
water. As the irrigation water applied to a crop increases 



CROP COMPOSITION 227 

the crude fiber remains practically constant in the leaves, 
increases rapidly in the stalks, and increases slowly in the 
underground parts. In hay crops the increase is not great 
so long as moderate quantities of water are applied, but 
when excessive quantities are applied, the crude fiber in 
all crops increases very rapidly. Woody crops are usually 
the result of over-irrigation. 

136. Color and flavor. — It is the general experience 
that lightly irrigated crops have the best color. Apples 
or peaches, grown with moderate quantities of water, 
are highly colored, while those receiving large quantities 
of water are of a paler color. Under conditions otherwise 
the same, the difference is not great, unless an excessive 
quantity of irrigation water be applied. The flavor of 
fruits is usually better when medium quantities of water 
arc used. In some crops, as wine grapes, this is of great 
importance. The flavor of the grape is transferred to the 
wine, and often determines the value of the beverage. 
When the irrigation water used is insufficient to produce 
a commercial crop, it often happens that small quantities 
of splendidly flavored fruit are obtained. In practice, 
the best' color and flavor are obtained when moderate 
quantities of water are used in irrigation. 

137. Flour. — The composition of the wheat kernel 
is strongly affected by irrigation. Much water produces a 
soft wheat; little water a hard wheat. High protein wheat 
is obtained with small irrigations; low protein wheat 
with large irrigations. This difference in the composition 
of the original kernel is transferred to all milling products 
of the wheat — bran, shorts and flour. For instance, 
in flour made from wheat grown with much water, there 
was 12.63 per cent of protein; with a medium amount of 
water, 12.92 per cent, and with no irrigation water, 13.62 



228 IRRIGATION PRACTICE 

per cent. Similar variations were found in all the essen- 
tial characters of the flour. Unquestionably, since millers 
demand hard and high protein wheat, the time is near 
when grain grown with much irrigation water will not be 
considered for flour-production on the markets of the 
world. Irrigated sections that still produce grain for 
flour should govern their irrigation practices in accord- 
ance with the needs of millers. 

138. Cooking value. — While very little definite infor- 
mation on the subject exists, it is fairly certain that the 
cooking value of fruits, vegetables and other crops is 
affected by the quantity of water used in irrigation. In 
one reported experiment, it seemed that potatoes grown 
with a medium quantity of water were whiter and mealier 
than were those grown with more water. Similarly, the 
flavor of vegetables is changed by the quantity of water 
used in irrigation. This is a very interesting field for 
investigation, especially by those interested in the food 
branch of home economics. 

139. Effect of cultural treatment. — It is evident from 
this discussion that the more moisture there is in the soil 
the higher the percentage of ash, carbohydrates and 
crude fiber, and the lower the percentage of protein. Any 
cultural treatment which results in maintaining more 
moisture in the soil during the growing period would, 
therefore, have the same effect as if more water had been 
added to the soil. The thorough cultivation of the soil 
to prevent evaporation conserves the moisture in the soil. 
In the Utah work, it was found that the percentage of 
protein was lower in crops grown on well-cultivated soils 
than in those grown on soils receiving little or no cultiva- 
tion. > Under the furrow method of irrigation, the per- 
centage of protein in the resulting crop was somewhat 



CROP COMPOSITION 



229 



higher than under the flooding method. However, the 
composition of the crop showed the greatest sensitive- 
ness to cultural methods in the matter of the time of 
applying irrigation water. Some of the results obtained 
are shown in the following table: 



Inches of 

irrigation water 

applied 


Time of application 


Per cent protein 

in dry matter 

of grain 


3.5 


At usual time. 


21.75 


3.5 


Later at time of "filling out." 


18.84 


7.5 
7.5 
7.5 


Two irrigations (5.0; 2.5) 
Two irrigations (2.5; 5.0) 
Two irrigations (3.75; 3.75) 


17.81 
16.65 
16.21 


10.0 
10.0 
10.0 


Two irrigations (7.5; 2.5) 
Two irrigations (2.5; 7.5) 
Two irrigations (5.0; 5.0) 


17.17 
16.40 
16.01 



Clearly, the response of the composition of the crop 
to the time of application is greatest when the total 
quantity of water used is small. It seems to be the invari- 
able rule that when the greater part of the water is applied 
early in the season, the percentage of protein is highest. 
On the other hand, when the distribution is such that 
the percentage of moisture remains constant throughout 
the growing season, the percentage of protein falls. When 
water is so applied that a high moisture period is followed 
by a low moisture period, the protein percentage increases. 
A more complete examination of this subject might go 
far in determining the time at which water should be 
applied. It offers an alluring field of experimentation 
for those engaged in irrigation study. 

The time at which grain is planted also helps to 
determine the composition of grain. When planted in 



230 IRRIGATION PRACTICE 

the fall, it grows partly in the fall, freezes down, and then 
grows again early in the spring, before the spring wheat 
is planted. Fall wheat has, therefore, a longer growing 
period than has spring wheat, and there is more water 
available for fall than for spring wheat. Consequently 
winter wheat contains a smaller percentage of protein 
than does spring wheat. In an experiment continued 
eight years, it was found that fall-sown wheat contained 
15.75 per cent of protein, whereas spring-sown wheat 
contained 16.85 per cent of protein. Similar differences 
have invariably been found when contrasting spring- 
grown and fall-grown grain. 

REFERENCES 

Jones, J. S., and Colver, C. W. The Composition of Irrigated and 
Non-Irrigated Fruits. Idaho Experiment Station, Bulletin 
No. 75 (1912). 

Le Clerc, J. A. A Comparison of Irrigated and Non-Irrigated 
Wheat. United States Department of Agriculture, Yearbook 
for 1906, p. 199. 

Lewis, C. J., Kraus, E. J., and Rees, R. W. Orchard Irrigation 
Studies in the Rogue River Valley. Oregon Experiment Sta- 
tion, Bulletin No. 113 (1912). 

Stewart, Robert and Hirst, C. T. Comparative Value of Irriga- 
tion and Dry-Farming Wheat for Flour-Production. Journal 
of Industrial and Engineering Chemistry, Vol. IV, No. 4, April, 
1912. 

Tollens, B. The Ash Constitutents of Plants. Experiment Station 
Record, Vol. XIII, Nos. 3 and 4. 

Widtsoe, J. A., and Stewart, Robert. The Chemical Composi- 
tion of Crops as Affected by Different Quantities of Irrigation 
Water. Utah Experiment Station, Bulletin No. 120 (1912). 

Widtsoe, J. A., and Stewart, Robert. The Effect of Irrigation on 
the Growth and Composition of Plants at Different Periods of 
Development. Utah Experiment Station, Bulletin No. 119 
(1912). 



CHAPTER XII 
THE USE OF THE RAINFALL 

Rain falls upon the whole surface of the earth Where 
there is much rain, the country is called humid; where 
there is little rain, the country is called arid. Humidity 
and aridity are conditions that depend, primarily, upon 
the water that falls from the heavens as rain or snow, 
although where water-dissipating factors, such as winds 
and shallow soils, are small, a low rainfall may be more 
effective than a high rainfall where these factors are large. 
Growing plants require large quantities of water. Some 
of this necessary water evaporates directly from the soil; 
another part evaporates from the leaves of the plant; 
some water may be lost, also, by seepage through the 
soil. Unless there is enough water in the soil, it is impos- 
sible for plants to thrive and to yield sufficient returns 
to the farmer. Irrigation is the art whereby the deficiency 
in the natural rainfall, whether large or small, is supplied 
by water, artificially added, so that regular, abundant 
crops may be obtained. 

140. Irrigation supplementary to rainfall. — Such a 
definition of irrigation makes it evident that the quantity 
of water to be used in irrigation depends on the degree of 
the natural precipitation. The higher the annual rain- 
fall that may be retained in the soil for crop use, the 
smaller the quantity of water required in irrigation. The 
lower the annual rainfall that may be so retained, the 
higher the irrigation requirement. This is a somewhat new 

(231) 



232 IRRIGATION PRACTICE 

thought in irrigation practice. Modern irrigation was 
founded in a very arid country, with almost rainless 
summers, at a time when there was no science of agricul- 
ture, and by men who had had no previous irrigation 
experience. The practice of irrigation was, therefore, 
founded on the assumption that irrigation was a primary 
art, practically independent of the natural precipitation. 
As practical irrigation experience was gathered it became 
clear that any rainfall, even a small one, if conserved in 
the soil, has crop-producing power, and that irrigation 
is always a supplementary art. Irrigation is and always 
should be supplementary to the rainfall. Consequently, 
the first big irrigation problem is to conserve the rain- 
fall in the soil for crop use, so that the available irriga- 
tion water may be made to cover as much ground as 
possible. The beginning of irrigation wisdom is the con- 
servation of the natural precipitation for the use of 
crops. 

141. Crop-producing power of rainfall. — The theoreti- 
cal productive power of the natural precipitation shows 
that even a low annual rainfall, properly conserved, may 
produce fair crops without irrigation. It has been shown 
previously that to produce one pound of dry matter on 
a fertile soil under arid conditions, more than 750 pounds 
of water are seldom required. If 750 pounds of water 
are required to produce one pound of dry matter, one 
bushel of wheat will require for its production 90,000 
pounds, or forty-five tons, of water. On this basis, each 
acre-inch of water — weighing about 113 tons — should pro- 
duce about two and one-half bushels of wheat. An annual 
precipitation of 10 inches, if fully conserved, should then 
produce twenty-five bushels of wheat per acre, which is a 
high average crop. 



USE OF THE RAINFALL 233 

142. Results of dry-farming. — This theoretical demon- 
stration has been well borne out by the results of the 
modern art of dry-farming. Dry-farming, as a system of 
agriculture, attempts to produce profitable crops without 
irrigation on soils that receive an annual rainfall of 
between 10 and 20 inches. Where there are high winds or 
other water-dissipating factors, a rainfall of from 20 to 30 
inches a year also requires dry-farming methods. The 
two-thirds of the area of the earth's surface receiving 
annually less than 20 inches of rain, are the so-called arid 
and semi-arid regions of the earth on which irrigation 
has been held, until lately, to be a necessity for success- 
ful crop-production. Yet, successful dry-farming, during 
the last few years, has been practised on great areas that 
receive between 10 and 20 inches of rainfall annually. 
This confirms the accuracy of the theoretical deduction 
of the crop-producing power of the rainfall. 

143. Crop value of rainfall in irrigation. — Experi- 
ments have also been performed to discover what propor- 
tion of a crop grown under irrigation may properly be 
credited to the natural precipitation. In the Utah work, 
the same crop was planted on two neighboring plots. 
One was irrigated; the other dry-farmed. Both plots 
yielded crops, and it was assumed that the yield on the 
plot receiving no irrigation was the same as the part of 
the yield under irrigation, due to the natural precipitation. 
Some of the results thus obtained are given in the follow- 
ing table. In reading the table, it should be remembered 
that the average precipitation under which the work was 
done was in the neighborhood of 15 inches a year. The 
soils were deep and of splendid water-holding power, and 
had been carefully tilled according to the best dry-farm 
methods, so as to conserve the natural precipitation. 



234 IRRIGATION PRACTICE 

Percent of a Crop Raised with About 7J^ Inches of Irri- 
gation, Due to the Natural Precipitation 

Per cent 

Wheat (grain) 83.99 

Wheat (straw) 86.42 

Oats (grain) 85.67 

Oats (straw) 98.19 

Corn (grain) 81.14 

Corn (stover) 83.03 

Alfalfa (all crops) 77.18 

Potatoes 66.89 

The results show that between 80 and 90 per cent 
of the yield of grain of wheat, oats and corn, grown with 
about 73^2 inches of irrigation water, was really produced 
by the natural precipitation. Even larger proportions 
of straw and stover were so produced. With the same 
degree of irrigation, 77 per cent of a crop of alfalfa, and 
67 per cent of a crop of potatoes, were produced by the 
natural precipitation. 

Bark and Welch carried on similar experiments on the 
Gooding Experiment Station, Idaho, with Blue Stem, 
Sonora and Little Club wheats. As an average of three 
years of work with these wheats it was found that of a 
crop raised with about 6 inches of irrigation water, about 
75 per cent of the yield should be credited to the natural 
precipitation. This confirms the Utah work. True, on 
different soils, the same precipitation would produce dif- 
ferent results, and these figures are probably maximum 
because of the excellent treatment given the soil and 
crops. However, a considerable proportion, usually from 
40 to 70 per cent, roughly one-half, of the crop obtained 
under irrigation may be safely credited to the natural 
precipitation, wherever the rainfall is over 12 inches 
annually and proper methods of cultivation are practised. 
On the other hand, when the rainfall is not conserved, the 



USE OF THE RAINFALL 



235 



yields under irrigation are greatly reduced. As the rain- 
fall is more carefully conserved, the area that may be 
served by the available irrigation water will be greatly 
increased. (Fig. 57.) 




Wheat 



Oars 



Corn 



Lvcer/7 



Potatoes 



Fig. 57. Yield of crops due to rainfall. Shaded areas, yields with irrigation; black 
areas, yields without irrigation. 

144. Conserving the rainfall. — The high crop-produ- 
cing value of the rainfall in irrigation practice makes it 
important to understand the best methods whereby the 
natural precipitation may be conserved. (1) The top 
soil must be kept in a loose condition, so that the water 
may enter the soil easily and completely as it falls from 
the heavens. (2) The soil must be so treated by thorough 
cultivation that the water which enters the soil will be 
kept there until needed by the plant. These are the two 
chief considerations of the irrigation farmer who desires to 
get the greatest possible returns from the rainfall. 

145. Distribution of rainfall. — The methods to be 



236 IRRIGATION PRACTICE 

employed in water conservation vary with the seasonal 
distribution of the rainfall. The rainfall varies not only 
from place to place, but varies also in its seasonal distribu- 
tion. Thus, on the Pacific seaboard, west of the Sierra 
Nevadas and the Cascades, the wet season extends from 
October to March, with a practically rainless summer. 
This is the Pacific type of distribution. Under the sub- 
Pacific type, which extends over eastern Washington, 
Nevada and Utah, the maximum rainfall is shifted toward 
the early spring, but the summers are still quite rainless* 
Under the Arizona type, fully developed in Arizona and 
New Mexico, about 35 per cent of all the rain falls in July 
and August, and May and June are generally the rainless 
months. Under the Rocky Mountain foothills type, 
most rain falls from April to June. Finally, under the 
Plains type, embracing the larger part of the Dakotas, 
Nebraska, Oklahoma and Texas, the heaviest rains come 
during May to July, when crops are growing. Moving 
eastward from the Pacific Coast to the Great Plains, the 
major rains are shifted from midwinter to midsummer. 
Moreover, in many places snow lies long on the ground 
in the winter, while in other places there is no snowfall. 
The methods of conserving the rainfall in the soil must be 
varied somewhat with regard to the prevailing type of 
precipitation. Whether rains come in winter or summer 
they must be stored in the soil for some time. Especially 
where the rains come in the winter, they must be held in 
the soil until the growing season arrives. 

146. Storing water in the soil. — Well-plowed soil is in 
a good condition to store water from the rains and snows. 
In the western United States, where the summers and 
falls are somewhat rainless, and the chief precipitation 
comes in winter or early spring, fall plowing is commonly 



USE OF THE RAINFALL 237 

resorted to for the purpose of enabling the rains to enter 
the soil. Fall plowing is practised as early as convenient, 
and the soil is frequently left in the rough throughout 
the winter. The fall, winter and spring rains are quickly 
absorbed by such land and stored to considerable depths, 
as already explained in Chapter III. Where the chief 
precipitation comes in late spring and summer, it is 
sufficient to plow in early spring and to keep the soil loose 
during the time of precipitation by tilling after each rain. 

147. Cultivation. — The purpose, effect and method of 
cultivation have been discussed in Chapter IV. It is the 
best known method for retaining the natural precipita- 
tion in the soil. It is just as important that the soil be 
carefully cultivated after a rain as after an irrigation. In 
the spring the land should be properly harrowed and culti- 
vated, so that the moisture gathered during the winter 
may not evaporate. 

148. Proportion of rainfall conserved. — In the inter- 
mountain country, where the precipitation comes in winter 
or early spring, it has been found that, by fall plowing 
and spring cultivation, from 60 to 90 per cent of the pre- 
cipitation between harvest and spring is found stored in 
the soil in the spring. In the region where the rainfall 
comes largely in spring and summer it has been found that 
it is possible to store in the soil during the summer sea- 
son from 40 to 60 per cent of all the moisture that falls 
at that time. Water so stored in the soil is of great value 
in producing crops; especially valuable is the water 
stored in the soil during winter, for it has been in very 
intimate contact with the soil particles and is heavily 
charged with plant-foods. 

149. Relation of irrigation- and dry-farming. — There 
is no opposition between dry-farming and irrigation- 



238 IRRIGATION PRACTICE 

farming. They are twin sisters. Upon them rests the 
responsibility of reclaiming the two-thirds of the earth 
which receive an annual rainfall of less than 20 inches. 
Newell estimates that under a perfected system of water 
storage, it is probable that not more than one-tenth of 
this vast arid region will be reclaimed by irrigation. The 
remaining nine-tenths must be reclaimed, if at all, by the 
methods of dry-farming. On the irrigated lands will be the 
great cities and the bulk of the population, but surround- 
ing them will be the great dry-farm empires, the products 
of which will help support the people on the irrigated 
tracts. Since, in any country, the supply of irrigation 
water is adequate to cover only a small fraction of the 
arid lands, it is important to learn every method whereby 
irrigation water may be made to render a high duty and 
to cover more land. The most promising method for 
accomplishing this result is the introduction into irriga- 
tion practices of methods whereby the natural precipita- 
tion may be conserved in the soil. That is, thorough and 
deep plowing in the fall, and frequent and deep cultiva- 
tion, should be made part and parcel of irrigation practices. 
When, in connection with this thorough tillage, irrigation 
water is applied in smaller quantities, so that larger returns 
may be obtained for each unit of water, it is not unlikely 
that the irrigated area may be increased three- or four- 
fold. From the beginning, therefore, the irrigation farmer 
should familiarize himself with the methods of dry-farming 
and apply them so far as may be possible in the develop- 
ment of a high duty of the available irrigation water. 

150. Dry-farm homesteads. — The dry-farming areas 
are often at considerable distances from large water sup- 
plies, although small springs or streams or subterranean 
waters are usually within reach. In some cases water 



USE OF THE RAINFALL 239 

must be hauled many miles to the dry-farms. The dry- 
farmer can do his work most effectively if he can build 
his homestead on the dry-farm and live there with his 
family. To do this he needs to have a small irrigated 
garden around his home, with some trees for shade and 
fruit. A clear understanding of the possibilities of irriga- 
tion water, combined with dry-farming methods, will make 
it possible to establish on the great majority of the dry- 
farms throughout the country small homesteads, where 
grass, and flowers and trees may be enjoyed. If, then, 
dry-farming methods are of value in extending the irri- 
gated area, the possibilities of small water supplies in irriga- 
tion will do much to make dry-farming more attractive 
to those who practise it. 

Dry-farming and irrigation will go hand in hand in 
redeeming the waste places of the earth. Both depend 
primarily upon the natural precipitation. 

REFERENCES 

Campbell, H. W. Soil Culture Manual. Soil Culture Company. 

Dry-Farming Congress, Reports of. 

Fortier, Samuel. The Use of Small Water Supplies for Irriga- 
tion. United States Department of Agriculture, Yearbook for 
1907, p. 409. 

Hilgard, E. W., and Loughridge, R. H. Endurance of Drought in 
Soils of the Arid Region. California Experiment Station, Bulle- 
tin No. 121; also (fuller), Report for 1897-8, p. 40 (1900). 

MacDonald, Wm. Dry-Farming. Century Company (1910). 

Mead, Elwood. The Relation between Irrigation and Dry-Farm- 
ing. United States Department of Agriculture, Yearbook for 
1905, p. 423. 

Merrill, L. A. Seven Years' Experiments in Dry-Farming. Utah 
Experiment Station, Bulletin No. 112 (1911). 

Shaw, Thomas. Dry Land Farming (1912). 

Widtsoe, J. A. Dry-Farming. The Macmillan Company (1911). 



CHAPTER XIII 
IRRIGATION OF CEREALS 

When land is brought under irrigation, the small 
grains form the first of the staple crops. This follows from 
the nature of the cereals. They furnish breadstuffs to 
man, and their by-products are excellent concentrated 
foods for farm animals. A ready market always awaits 
the small grains, and they bring, therefore, sure and quick 
returns to the farmer who is just beginning the conquest 
of an irrigated farm. The small grains mature at the time 
of large water supply, and for that reason, need less atten- 
tion during the drier period of the growing season. Land 
is easily prepared for small grains and the cultural opera- 
tions are simple. After more profitable crops have been 
established under the irrigation system, the small grains 
fit well into the rotations necessary for the maintenance 
of soil fertility. Finally, small grains may be grown with 
limited capital, which is all-important to the average new 
settler. 

In the beginning of irrigation in the United States, 
the small grains formed the bulk of the crops that were 
raised. Extensive grain-growing under irrigation is, 
however, gradually ceasing, because special crops, such 
as sugar beets and fruits, yield larger acre returns than 
the grains, and, moreover, because it has been shown that 
the small grains are particularly well adapted for growth 
under dry-farming methods on the non-irrigated lands. 
Then, the increasing demand by millers for hard wheats 

(240) 



IRRIGATION OF CEREALS 241 

will gradually diminish the market value of the softer 
wheats produced by irrigation. 

Undoubtedly, small grains, especially wheat, as a 
major crop, will gradually be driven from the irrigated 
to the non-irrigated lands, although they will always 
be important crops, since they fit well into rotations. 
Wherever an irrigation enterprise is begun, it will be 
found profitable to grow, for some years, extensive crops 
of the small grains. 

.151. Spring vs. fall wheat. — Wheat may be considered 
as a type of the small grains. Formerly, under irrigation 
practice, spring grains were sown almost entirely. With 
the advance of dry-farming, which is characterized by fall 
sowing, irrigated grain is often planted in the fall. The 
advantage of fall planting is that grain so sown makes 
better use of the fall and winter precipitation, gets an 
early start in the spring, and matures earlier. Moreover, 
less water is required to bring the fall grain to maturity 
and to a high yield. In harmony with the spirit of econo- 
mizing irrigation water, the sowing of fall grain should be 
made a general practice in irrigated sections. 

152. Quantity of wheat to sow. — The quantity of 
seed to sow must be varied with the quantity of irriga- 
tion water available throughout the season. Under dry- 
farming, on lands that receive an annual precipitation of 
12 to 15 inches, twenty-five to thirty pounds of wheat are 
used to the acre. Under irrigation, with the same annual 
rainfall, one to three bushels of seed or more are often 
used. It is not wise to use too much seed, for the numerous 
plants that result demand a large supply of water, if they 
are to be brought to maturity; and, if by chance the water 
supply should be cut off or diminished, the excessive num- 
ber of plants would speedily exhaust the soil moisture 
p 



242 IRRIGATION PRACTICE 

m 

and become seriously injured. A common experience on 
dry-farms, where too much seed has been used, is to find a 
splendid stand of young grain in the spring, and failure 
at harvest time. Under irrigation, as under dry-farming, 
the number of plants must be proportional to the proba- 
ble water supply. If the number of plants is in excess 
of the probable water supply, the yield will be unsatis- 
factory. It is always better to sow limited quantities 
of seed, for by stooling there is an automatic adaptation 
of the wheat plant to the water in the soil. Experiment 
has shown that where little seed has been sown, and the 
water has been sufficient, the harvest is as great as if 
more seed has been sown. No material change in the 
acre-yield has occurred even when the seed sown to the 
acre varied from four to twelve pecks. One bushel or less 
is probably as satisfactory as larger quantities, except on 
very rich soils with an abundance of water. 

153. Method of sowing wheat. — Wheat and the other 
small grains should always be planted in rows by some 
one of the many press drills. This enables the farmer to 
control the quantity of seed used, and the depth and 
regularity of planting. Under irrigation, the yield is 
influenced by the distance between the drill rows. Experi- 
ments on this subject indicate that the yield is increased 
when the same quantity of seed to the acre is planted in 
rows twice as far apart. This may be due to the greater 
chance, under such conditions, of a large lateral develop- 
ment of the roots. 

The direction of the drill rows may be of considerable 
importance. On comparatively level land, the drill rows 
may help guide the irrigation water from place to place. 
On rolling land and steep hillsides the drill rows may be 
run with the contour lines, i. e., across the inclination. 



IRRIGATION OF CEREALS 243 

By this method, the rows become checks to the descend- 
ing water, and washing or unnecessarily rapid flooding 
of the land is prevented. 

154. Cultivation of wheat. — As explained in Chapter 
IV, cultivation, properly performed, may largely take the 
place of irrigation. On clayey soils there is a tendency 
for a crust to form after each irrigation, which should be 
broken to prevent serious injury to the plants. The present 
system of planting grains in rows very near each other 
makes it difficult and probably unprofitable to give such 
crops inter-row culture. However, wheat fields may 
safely be cultivated while the plants are young — from 8 
to 12 inches high — by harrowing with an ordinary spike- 
tooth harrow with the teeth set backward, so that few 
plants will be torn out. The corrugated roller is some- 
times used to break the crust, but the harrow is probably 
better, since it does not compress the soil. As the grain 
becomes older it shades the ground very completely, and, 
consequently, baking of the soil is not so common later 
in the season. 

155. Method of irrigating wheat. — Water may be 
applied to wheat by any of the standard methods of irri- 
gation. In the beginning of American irrigation, flooding 
was almost the only method employed. Only gradually, 
to meet compelling conditions, was the furrow method 
thought out and adopted and, even today, flooding is the 
most general method of irrigating wheat and other small 
grains. The. flooding of grain is accomplished ordinarily 
by the field-ditch method. From the main supply ditch, 
smaller ditches, often following the high lines or ridges, 
are taken out to the field. From these again, small tem- 
porary field ditches or mere furrows are made, from which 
the water overflows to cover the land. Occasionally, but 



244 



IRRIGATION PRACTICE 



only where there is an abundance of water, the small 
grains are irrigated by the check or basin system. The 
furrow method of irrigating the small grains is rapidly 
coming into use, and promises to displace the more 
extensively used flooding methods. Under the flooding 
method, much labor is required to apply the water to the 
land, but little labor to prepare the land for irrigation. 
Under the furrow method little labor is needed to apply 
the water, but the land must be carefully prepared before 
the method can be employed. 

The method to be chosen depends on the soil and the 
scarcity of water. Lands with a baking tendency, sown 




Fig. 58. Irrigating wheat. 

to grain, as already suggested, are cultivated with diffi- 
culty. When the furrow method is employed on such 
lands, only the soil touched by the water in the furrows 
bakes, and cultivation is not so necessary. Other lands 
wash easily. They are usually of very fine texture, and 
are rich either in calcium sulphate with other somewhat 



IRRIGATION OF CEREALS 



245 



soluble substances or are derived from volcanic ash. Even 
a small stream of water, with a slight fall, running on 
such soils, unless watched with extreme care, may quickly 
cut deep ravines and destroy the field. On such soils, there- 
fore, the furrow method, which permits of a better con- 




Fig. 59. Canvas clam to check water. 

trol of water, is gradually becoming the only method. 
Limited supplies of irrigation water also demand the fur- 
row method, for it is evident that, with a given quantity 
of water, more land may be covered by the furrow than 
by the flooding method. It has been explained that the 
yield of a crop to a unit of water is greater when small 
quantities are used and a larger total yield will be obtained 
when the small available quantity of water is spread over 
a large area. 

Finally, under the best flooding system it is difficult 
to secure an even distribution of water over ordinary 
lands, which are not absolutely level. The furrow method 
permits of a more even, though not by any means per- 
fectly even distribution. This has been another determi- 
ning factor in the acceptance of furrow irrigation for small 
grains. 



246 IRRIGATION PRACTICE 

The furrows are usually made after seeding but before 
the plants come up, by the use of special implements 
described in Chapter XX. Shallow furrows, usually 5 
inches deep and from 6 inches to 3 feet apart, are ordi- 
narily employed. Their length varies from 150 to 600 feet, 
depending on the slope, the nature of the soil and various 
other conditions. Long furrows are of doubtful value, 
for the upper end of the furrow receives water for a longer 
time than does the lower end, and, consequently, in long 
furrows the upper end may be over-irrigated when the 
lower end has received just enough. Shorter furrows 
obviate this danger, at least in part. (Figs. 58, 59.) 

156. Time of irrigating wheat. — The time of irriga- 
tion, one of the most important factors in the economical 
use of water, depends in part upon the distribution of the 
rainfall throughout the year. Land for spring grain is 
especially suitable for fall and winter irrigation. Such 
lands, when plowed in the early fall and given a good 
soaking in the fall, will contain much stored water in the 
spring to germinate the seed and to maintain the young 
plants far into the early summer. However, fall and win- 
ter irrigation is to be considered only when the natural 
winter precipitation is insufficient to saturate the soil to 
a depth of 8 to 10 feet. It is especially in districts where 
the precipitation comes largely in spring and the growing 
season, and where the winter and fall are dry, that irri- 
gation during the dormant season is of much value. 

When the soil enters the spring in a somewhat dry con- 
dition, it becomes necessary to provide by irrigation the 
water needed for germinating the seed. This may be 
accomplished by applying a thorough irrigation to the 
soil before seeding, after which the land is plowed, 
then sown to the crop. The objection to this method is 



IRRIGATION OF CEREALS 247 

the delay occasioned by the necessary interval between 
irrigation and plowing. For that reason, the soil is fre- 
quently plowed early in the spring, irrespective of dry- 
ness, the seed planted in the dry soil, and then irrigated. 
The water thus added immediately favors germination 
and furnishes also a supply of water for the young plant. 
Both of these methods of early irrigation are giving satis- 
factory results. 

After germination and first growth, irrigation should be 
delayed as long as possible. When water is needed, the 
grains, which normally are of a light green color, become 
darker green, and in protracted dryness the lower leaves 
become definitely yellow. If the soil becomes too dry, 
the crop may be permanently injured; in fact, the soil 
below the surface should remain fairly moist throughout 
the growing season. If the seed has been planted in well- 
saturated soil, since young plants require little moisture, 
several weeks will elapse before irrigation will be necessary. 

During the early stages of growth, the plant devotes 
its energies to the preparatory work of gathering carbon 
from the air and mineral matters from the soils, and of 
combining these into organic forms. The period of most 
rapid growth comes shortly before or at the time of flower- 
ing. At the time of "boot," that is, when the heads just 
begin to show, it is well to apply water, and again, if 
needs be, at the time of seed-formation. It is most impor- 
tant, however, that the soil be not dry at the time of 
flowering; for, if there is an abundance of water at that 
time, a ready transfer of nutritive materials from stalks 
and leaves to the heads is made possible. Moreover, 
water applied when the seeds are "filling out" will result 
in increased grains at the expense of the straw. 

It may be that the answer to the question concerning 



248 IRRIGATION PRACTICE 

the right time of applying water to grain is to keep the 
soil approximately at the same moisture content through- 
out the season, until ripening sets in. Some authorities 
have declared that plants need a high soil-moisture per- 
centage at one period and a smaller one at another period 
and so on throughout the season. This may be correct, 
but in practice the farmer will make no mistake in main- 
taining the soil in approximately the same correct mois- 
ture condition throughout the season. More water will 
be transpired, and the irrigations therefore heavier or 
more frequent at the time of most rapid growth, that is, 
about the time of flowering. 

It is seldom necessary to give wheat more than three 
irrigations except, possibly, in the hot climate of Arizona 
and similar regions. In fact, two irrigations are usual, and 
one irrigation ordinarily ample wherever the annual 
precipitation is between 12 and 15 inches. Where the 
annual precipitation is large, little water will be required; 
where it is small, much water must be added by irriga- 
tion. Bark found that under a rainfall of about 18 inches, 
the water used for grains by farmers during the months 
of May to August inclusive, was as follows: May, 7.86 
per cent; June, 52.34 per cent; July, 36.14 per cent; 
August, 3.66 per cent; total, 100 per cent. In the moun- 
tain country, where grain is sown in April, there is little 
need of irrigation after late June or earliest July. Fall- 
sown grain, with proper tillage, needs probably only one 
heavy irrigation, or at the most two light irrigations. 
McLaughlin recommends that wherever weeds have been 
troublesome the grain fields be irrigated after harvest, to 
germinate the weed seeds, and later to plow the plants 
under. Thus, the soil is fertilized and the weeds destroyed. 

157. Quantity of water for wheat. — The quantity of 



IRRIGATION OF CEREALS 



249 



water to be used for wheat and the small grains depends 
upon many factors. Less water is required on clayey 
than on sandy or gravelly soils. Deep soils require less 
water than shallow soils, or soils underlaid by gravel or 
hardpan. Bark, working in Idaho, found that, in actual 
practice, grains received on medium clays and sandy 
loams about 18 inches of water, while on sands or gravelly 
soil nearly 36 inches were used. More water is necessary 




Fig. 60. Irrigated wheat in Montana. 

on new than on old land. A high temperature, a low 
relative humidity and a steady wind increase the water 
requirements of crops. All these and others previously 
discussed, must be considered in deciding on the quantity 
of water to be used. 

The fundamental law to be considered in determining 
the quantity of water used in the production of wheat and 
of other crops is that, as more water is applied to a field 
the smaller is the relative yield of grain and of straw. 
Undoubtedly, as water is applied, the total yield increases 



250 



IRRIGATION PRACTICE 



steadily to a limit, beyond which there is an actual 
decrease; but, as the increase goes on, there is a steady 
diminution in the yield per unit of water applied. This is 
shown in the following table, taken from the Utah results: 

Yields of Wheat with Varying Quantities of Irrigation 

Water 



Inches 
of irrigation 


Bushels of 
grain 


Pounds of 
straw 


Pounds of 
straw for 


Bushels of 
wheat for 
each inch 


water applied 


to the acre 


to the acre 


of grain 


of water 


5.0 


37.81 


2,986 


79 


7.56 


7.5 


41.54 


3,301 


75 


6.39 


10.0 


43.53 


3,452 


79 


4.35 


15.0 


45.71 


3,954 


87 


3.05 


25.0 


46.46 


4,311 


93 


1.86 


35.0 


48.55 


4,755 


98 


1.39 


50.0 


49.38 


5,332 


108 


0.99 



The quantity of water applied to wheat varied from 
5 to 50 inches, but the yield varied from about thirty- 
eight bushels to a little over forty-nine bushels — an 
increase of not quite twelve bushels of wheat for an 
increase of nearly 45 inches of water. In the last column 
of the table, it is shown that the yield per inch of irriga- 
tion water fell from about seven and one-half bushels with 
5 inches of water, to about one bushel with 50 inches 
of water. This variation in yield, due to increasing applica- 
tions of water, has been confirmed by practically every 
investigator who has carried on accurate work under 
field conditions. Moreover, the greater the quantity of 
water used, the smaller the proportion of seed in the whole 
plant. See the fourth column of the above table. (Fig. 63.) 

Not only is it possible to diminish beyond serious con- 
sideration the acre-inch yield by increasing irrigations, 
but it is possible by excessive irrigation to cause an actual 



IRRIGATION OF CEREALS 



251 



decrease in the total yield. Further, an excess of water 
delays ripening, and thus subjects the grain to the dangers 
of late growth when the fall frosts are at hand. When too 
much water is used, the plant becomes converted into a 
pumping system, having for its purpose the ridding of the 
soil of the injurious excess of moisture. Such over-irriga- 
tion is, naturally, less likely to occur on porous than on 
compact soils; but, on the other hand, the excess of water 







\dm£*?* 
























f 


|L JS^-*. : '- v aife- 


, 


- 


« 


•';<■• v' - 





Fig. 61. Irrigated oats in Montana. 

applied to porous soils moves downward more easily to 
raise the standing water table. Fortunately for the 
pioneers who laid the foundations of irrigation, and who 
were not well acquainted with the dangers of over-irriga- 
tion, the small grains endure fairly well an excess of 
water. Wheat can probably endure over-irrigation better 
than either oats or barley. However, the practice is un- 
wise; and the ridiculously large quantities of water often 
applied in the hope of large yields are a serious menace 
to the permanence of irrigation agriculture. 



252 



IRRIGATION PRACTICE 



The quantity of water which produces the largest 
yield of grain to the acre is seldom the most economical 
quantity to apply. In the irrigated region, the acre of 
land and the acre-foot of water must both be given atten- 
tion; and, since the acre-foot of water usually has a higher 
value than the acre of land, the emphasis should be 
placed upon the producing power of a given volume of 
water. The possibility of wheat-production with 30 
acre-inches of water — the quantity often assigned by 
irrigation engineers — based on the preceding table, may 
be shown as follows: 





30 acre-inches spread over 




1 acre 


2 acres 


3 acres 


4 acres 


6 acres 


Grain 

Straw 


47.51 
4,532 


91.42 
2,908 


130.59 
10,256 


166.16 
13,204 


226.16 
17,916 



By spreading 30 acre-inches over 6 acres instead of 
over 1, the total yield of wheat was increased from forty- 
seven bushels to 226 bushels. In the final establishment 
of empires on irrigated soils this fundamental relation- 
ship between water and crop-yield, must of necessity be 
taken into consideration. (Fig. 64.) 

The best knowledge of the day makes it safe to say 
that, on deep soils, 73^2 inches of water in two good irriga- 
tions, should be ample for the production of a crop of 
wheat. On shallow, gravelly soils, as high as 18 inches 
may be used in four or five irrigations. On many soils 
one good irrigation of 4 to 5 inches would be sufficient to 
carry the crop to a large yield of grain of higher quality 
than if more water were used. Everything considered, 
an average of 1 acre-foot should be ample for the pro- 
duction of wheat on fertile, well-tilled soils. 



IRRIGATION OF CEREALS 



253 



If 12 acre-inches be taken as the quantity of water 
amply sufficient for the needs of wheat, the subjoined 
table shows that 1 second-foot, during a sixty-day irri- 
gation period, will cover 120 acres; during a forty-five- 
day irrigation period, 90 acres. If 7J^ inches be the 
depth of water applied, the duty of a second-foot will 
vary as shown below from 60 to 192 acres. In many 
places in the West, the duty of water for grain has been 
raised to 200 acres or more. For instance, under the 
famous Bear River Canal of Utah, where irrigation prac- 
tices have been worked out to great perfection, Wheelon 
reports that there is a gradually decreasing duty of 
water for grain and for all other crops. At the present 
time the duty of water there approximates 170 acres for 
grain with a prospect of a rapid increase. 



Duty in Acres 


of Second-Foot of Water Continuously 
Flowing 


Depth of water 
applied 


-- - 

Length of irrigation 
season 


Duty 


7.5 inches 
7.5 " 

12.0 " 
120 " 

18.0 " 
18.0 " 


45 days 
60 " 

45 " 
60 " 

45 " 
60 " 


144 acres 
192 " 

90 " 

120 " 

60 " 
80 " 



158. Oats. — Oats is another of the staple crops of the 
irrigated section. It has almost always been sown in the 
spring, but the development of dry-farming has led to the 
introduction of winter varieties. It is very probable that 
oats, like wheat, will, in the future be grown chiefly under 
dry-farming, although the crop will find an important 



254 



IRRIGATION PRACTICE 



place in the rotations for maintaining the fertility of 
irrigated land. 

In general, oats and wheat may be treated alike. The 
quantity of seed should be carefully regulated with respect 
to the available water. The cultivation, methods and 

Iain canal.80TeeTWIdE; 

■HIM -: lume. WAG s = •'• D 





DRAINAGE DITCH. 

Fig. 62. Plan of rice irrigation. 

time of irrigation are practically the same as those dis- 
cussed under wheat. The duty of water for oats is about 
the same as for wheat, although oats is rather more sensi- 
tive than wheat to over-irrigation. Oats of high quality 
may be grown abundantly by the moderate appli- 
cation of water. We are quite safe in saying that the 



IRRIGATION OF CEREALS 255 

duty of water for oats should not be any lower than 
for wheat. 

159. Barley. — Barley is also a valuable crop for irri- 
gated lands. Excellent malting barley is produced under 
irrigation, and, in fact, irrigated barley appears to be the 
best for malting. The irrigation of barley conforms with 
the irrigation of wheat or oats. Barley is even more sen- 
sitive than oats to over-irrigation, and water should, 
therefore, be applied to barley with great care. In the 
Utah work it was found that the total yield of barley 
did not increase, or decrease, after a depth of 7J^ inches 
of water had been applied. In the Wyoming work, little 
increase was found after 16 to 20 inches had been applied 
However, it has been demonstrated that the malting value 
of barley decreases when too much water is applied in 
irrigation. The duty of water for barley should not be 
lower than for oats or wheat. 

160. Rye. — Rye is seldom grown under irrigation, for 
it does so well under dry-farming that there is no good 
reason for using costly irrigation water in its production. 

Wheat, oats, barley and rye behave very much the same 
in their relation to water. The chief difference is in the sen- 
sitiveness to water. Wheat endures more water than oats, 
and oats more than barley, and barley probably more than 
rye; but, practically, the effect of irrigation on these crops 
is the same. All of them have a larger proportion of straw 
in the whole plant, if grown with much water. 

161. Corn. — Corn, the great American crop, thrives 
and yields heavily under irrigation. It produces more 
dry matter for the water used than practically any other 
crop, and, when drought comes, it survives and produces 
fair yields. Dry-farm corn seldom fails. The importance 
of the corn crop to the irrigated region will increase rapidly 



256 



IRRIGATION PRACTICE 



as its behavior under irrigation becomes better under- 
stood, and as dairying and other forms of animal hus- 
bandry develop on irrigated lands. 

Corn differs from the small grains in its longer growing, 
hence longer irrigating, period. The details of prepar- 
ing the land, seeding and general cultural practices are 




Fig. 63. Yield vs. water (wheat). 

those followed in humid districts. Drill or row culture is 
the only allowable method of sowing corn under irrigated 
conditions. 

Cultivation is as essential in corn-growing under 
irrigation as under humid conditions. The soil should be 
cultivated immediately after each irrigation, as soon as 
the soil is dry enough to permit the hoe to be safely 
used. Moreover, it is well to cultivate the corn at least 



IRRIGATION OF CEREALS 



257 



twice to four times between irrigations. By this method 
the water-cost of the crop may be greatly reduced. More- 
over, thorough cultivation yields a corn crop having a 
much higher feeding value than one which has received 
less thorough cultivation. 

Irrigation water is invariably applied to corn in fur- 
rows, although the flooding methods may be used. Since 




jOsrer* 




Ow7tvo/7ca: 










WKk Grain WWi Straw 

Fig. 64. Producing power of 30 acre-inches (wheat). 

corn is inter-tilled, it is much more convenient and satis- 
factory to irrigate by the furrow method and, further, 
the corn plant should not be in contact with water. The 
furrow is dug half way between the rows. For reasons 
already discussed the furrows should not be made too 
long. 

Corn land may well be irrigated in the fall and winter, 
if the natural precipitation during those seasons is not 
sufficient to saturate the soil thoroughly. The soil should 
Q 



258 IRRIGATION PRACTICE 

be well stored with moisture at the time of seeding, and 
when this is not the case it may be necessary, as in the 
case of wheat, to give the soil a thorough soaking before 
planting. 

162. Time to irrigate corn. — Corn is planted later 
than the small grains and during its early growth is, 
therefore, subjected to a higher temperature and more 
rapid evaporation. However, the young plant draws little 
water from the soil, and the first irrigation after seeding 
should be light and should come as late as possible. As 
the plant continues its growth the irrigations may be 
increased in quantity and frequency. The May planting 
of corn means that July and the first half of August are 
the periods of most rapid growth and during which most 
irrigation is needed. After August 15, less water is 
required; in fact, it is questionable if water should be 
applied to corn after the period of August 15 to September 
1. As in the case of the small grains, the key to the suc- 
cessful production of irrigated corn seems to be to keep 
the soil in a uniform moisture condition throughout the 
season. It is manifestly impossible under irrigated con- 
ditions to keep the soil exactly at the same percentage of 
moisture; but, by proper cultivation and irrigations at 
correct intervals, the soil may be maintained throughout 
the season at a favorable moisture percentage. Excessively 
dry and wet periods should never follow each other. 

Corn, like the small grains, should have at its disposal 
an abundance of water at the time of seed-formation. When 
the seed is ripening, little water is required; in fact, in 
the later periods of growth, water must be withheld from 
the plant, so that ripening may not be delayed. If little 
water is available during the season, two irrigations are 
probably sufficient, and two are better than one. In one 



IRRIGATION OF CEREALS 259 

series of Utah experiments it was found that 7 x /2 inches 
applied in one irrigation yielded nearly ninety-two bushels 
of corn; whereas, the same quantity of water applied in 
two equal irrigations yielded nearly 102 bushels of corn. 
When the two irrigations were used, there was a larger 
proportion of seed in the whole plant, indicating that an 
application of water was made possible at the time of 
seed-formation, and nutritive materials were probably 
transferred to the ears at the expense of the stover. An 
annual precipitation of 12 to 15 inches coming largely in 
the fall and spring would indicate that three irrigations 
throughout the season should be sufficient to mature a 
good crop of corn. True, many farmers apply water more 
frequently than this, but the greater number of irrigations 
is of doubtful value. Fewer irrigations, with many culti- 
vations, would in the end be more satisfactory. When 
four or five irrigations are applied, about 10 per cent of 
the total water should be added in June; 50 per cent in 
July; 30 to 40 per cent in August, and about 10 per cent in 
September. When only two irrigations are applied, per- 
haps 60 per cent of the total should come early in July. 

163. Quantity of water for corn. — Corn is not a water- 
loving crop. It will use large quantities of water if avail- 
able, but it does not demand an abundance of water to 
produce a good yield. As with other crops, the soil 
determines chiefly the quantity of water used by the 
corn crop. On shallow, gravelly and new soils, more water 
is necessary than on the deep, clayey, well-tilled soils. 
The climatic factors that increase evaporation increase 
the water-use of the crop. 

Corn, like all other crops, is subject to the law that 
the increase in yield is not proportional to the increasing 
water supplied by irrigation. The more water is used, 



260 



IRRIGATION PRACTICE 



though the total yield be slightly larger, the less the yield 
to the unit of water. The following table, taken from the 
Utah work, will illustrate this statement: 

Yields of Corn with Varying Quantities of Irrigation Water 



Inches 

of irrigation 

water applied 


Bushels of 

grain 
to the acre 


Pounds of 

stover 
to the acre 


Pounds of 

stover to 

one bushel 

of corn 


Bushels of 
grain for 
each inch 
of water 


7.5 


79.14 


7,189 


91 


6.07 


10.0 


89.52 


6,007 


67 


5.80 


15.0 


93.93 


8,279 


88 


4.57 


20.0 


91.58 


8,692 


95 


3.59 


25.0 


99.16 


9.492 


96 


3.25 


30.0 


97.12 


10,390 


107 


2.73 


55.0 


96.78 


10,258 


106 


1.43 



The depth of irrigation varied from 73^ to 55 acre- 
inches, but the acre yield increased only from eighty to 
ninety-seven bushels of grain, and the stover showed a 
similarly small increase. The bushels of grain per inch 
of irrigation water were six, when 73^2 inches of water 
were used; and only 1.43, when 55 inches were used — a 
decrease of three-fourths. Invariably, also, as more water 
was used, the proportion of stover to grain increased. 
(Fig. 65.) 

Thirty acre-inches have been allowed, frequently, by 
state engineers as the proper quantity of water to be used 
by farmers. It may be calculated from the above table 
that, when 30 acre-inches are applied to 1 acre, about 
ninety-seven bushels of corn are obtained; when spread 
over 4 acres, more than 316 bushels of corn are produced. 
This possible crop-producing power of water must be con- 
sidered in building irrigated empires. The best knowledge 
of the day indicates that 12 to 15 acre-inches are ordi- 
narily a very satisfactory depth of water for the produc- 



IRRIGATION OF CEREALS 



261 



tion of good crops of corn. The longer growing season of 
corn makes necessary more irrigations and possibly a 
larger quantity of water than for wheat. Where the rain- 
fall is less than 12 inches, or on unfavorable soils, or under 
conditions of very high evaporation, it may be necessary 
to increase this quantity of water to 18 inches. It is more 
likely, however, that on deep soils, properly cultivated, 
the depth of water necessary to produce proper crops of 
corn may be reduced to 10 or even 73^ inches of water. 

If it be assumed that the length of the irrigating sea- 
son for corn is ninety days, the duty of a second-foot 
should not be greatly different from that of wheat. One 



JJOr 






Com 






JO 



rrrnrri 
i mm 




Fig. 65. Yield vs. water (corn). 



262 



IRRIGATION PRACTICE 



second-foot, flowing for ninety days, will cover 180 acres 
to a depth of 12 inches. This corresponds closely to the 
duty of water as given for wheat. As in the case of the 
small grains, the duty for corn is steadily increasing. 




Fig. 66. Irrigated corn in Arizona. 

164. Rice. — Rice is a semi-tropical plant, best devel- 
oped in moist climates. Certain varieties of upland rice 
thrive in dry climates, but these are practically unknown 
in the United States. The rice of commerce requires 
moist conditions, and, therefore, heavy irrigation. It is 
grown chiefly on the delta and marsh lands of the South 



IRRIGATION OF CEREALS 263 

Atlantic States, the alluvial lands along the Mississippi, 
and in southwest Louisiana and southeast Texas. Upland 
rice may be grown wherever corn does well, and by 
methods similar to those used in the culture of summer 
oats. 

Rice fields are divided by field levees into tracts of 
varying sizes, depending on the slope of the land and the 
depth of water to be applied. When the water is to stand 
over the field from 6 to 12 inches deep, the levees are 
made from 12 to 18 inches high; they should, in fact, be 
just high enough to retain the water at the depth decided 
on. If the levees are too large, the resulting vegetation on 
them is a source of annoyance. The method of irrigation 
is necessarily the method of checks. 

Immediately after seeding, the land is flooded for a 
few days. When the plants are 6 to 10 inches high, they 
receive the first irrigation. From that time the water is 
made to stand on the land to a depth of 3 to 6 inches until 
the grain is in the dough, or about two weeks before har- 
vest, when the water is drained off and the crop left to 
ripen. The irrigation water is nearly always pumped from 
lower levels into the checks, and the ground water is 
very near the surface, so that it is not a difficult matter 
to keep water standing on the soil for any desired length 
of time. The length of the irrigation season varies from 
two to three months, with an average of about seventy 
days. 

It might be supposed, from the fact that rice fields are 
thus covered with standing water, that large quantities of 
water are necessary for rice-production. The careful 
investigations of the Office of Experiment Stations show 
that only from 12 to 18 inches of water above the rainfall 
are really used by the plant. In one series of experiments, 



264 IRRIGATION PRACTICE 

about 29 acre-inches of water were applied throughout 
the season to the field, including the rainfall ; the evapora- 
tion was about 16 inches, leaving 13 inches that were 
actually used by the plant. This is not greatly different 
from the quantity of water actually supplied, by irriga- 
tion, to other cereals. 

The rice industry is very old in the United States. 
For many years it had languished, but of recent years 
has, appeared to show signs of new growth. It is probable 
that the study of varieties of rice suitable for growth on 
the great irrigated areas of the country, where less water 
must be used, may develop another highly profitable 
branch of industry for the irrigated region. (Fig. 62.) 

REFERENCES 

Bark, Don H. Duty of Water; Investigations (1910-12). Ninth 
Biennial Report, State Engineer of Idaho (1912). 

Bond, Frank, and Keeney, George H. Irrigation of Rice in the 
United States. United States Department of Agriculture, Office 
of Experiment Stations, Bulletin No. 113 (1902). 

Harris, F. S. The Irrigation and Manuring of Corn. Utah Experi- 
ment Station, Bulletin (1914). 

Humbert, Eugene P. Wheat-growing Under Irrigation. New Mex- 
ico Experiment Station, Bulletin No. 84 (1912). 

Hunt, Thomas F. The Cereals in America. Orange Judd Company 
(1904). 

McLaughlin, W. W. Irrigation of Grain. United States Depart- 
ment of Agriculture, Farmers' Bulletin No. 399 (1910). 

McLaughlin, W. W., and Morgan, E. R. Irrigation Investigation 
during 1905-6. Utah Experiment Station, Bulletin No. 99 
(1906). 

Nowell, Herbert T. Irrigation of Barley. Wyoming Experi- 
ment Station, Bulletin No. 77 (1908). 

Teele, R. P. Review of Ten Years of Irrigation Investigations. 
United States Department of Agriculture, Office of Experi- 
ment Stations, Annual Report for 1908 (separate). 



IRRIGATION OF CEREALS 265 

Welch, J. S. Irrigation Practice. Idaho Experiment Station, Bul- 
letin No. 74 (1914). 

Widtsoe, J. A., and Merrill, L. A. Methods for Increasing the 
Crop-producing Power of Irrigation Water. Utah Experiment 
Station, Bulletin No. 118 (1912). 

Widtsoe, J. A., and Merrill, L. A. The Yields of Crops with 
Different Quantities of Irrigation Water. Utah Experiment 
Station, Bulletin No. 117 (1912). 



CHAPTER XIV 

ALFALFA AND OTHER FORAGE CROPS AND 

PASTURES 

A permanent, modern system of agriculture cannot 
be developed without the aid of live-stock husbandry. 
Consequently, forage crops and pastures are of high 
importance in irrigation agriculture. However, no forage 
crops of any kind should be shipped out of the dis- 
trict where they are raised, for the plant-food contained 
in hays, especially alfalfa hay, is often worth more than 
the money actually received for the hay. Irrigation- 
farmers, dealing with a new and largely undeveloped 
system of agriculture, on very fertile soils, are tempted 
to pay little or no attention to the permanence of the 
system. In the sections recently reclaimed by irrigation, 
there is, however, the most unusual opportunity known 
in the history of agriculture, to apply our vast, new agri- 
cultural knowledge on lands which never before have 
been under cultivation. It should be possible by the wise 
use of our knowledge to build, under irrigation, a system 
of agriculture excelling all others in profitableness and 
increasing fertility. A first principle in accomplishing 
this is that the irrigated sections must send out only such 
products as have been manufactured from the rougher 
crops — butter, cheese, sugar and meats — and which con- 
tain the minimum quantities of plant nutrients. 

165. Alfalfa, or lucern. — This wonderful crop has 
been the foundation of successful irrigation agriculture 

(266) 



ALFALFA, FORAGE CROPS AND PASTURES 267 

in the United States. If corn is the king, then alfalfa is 
the queen of American crops. Alfalfa is of high antiquity, 
and the watchful care of unnumbered generations of 
farmers has resulted in a crop of extremely high agri- 
cultural value. It thrives best in arid and semi-arid 
climates, and under irrigation in such climates reaches 
its highest perfection. Differences in altitude or average 
temperature do not affect it much, so that over the whole 
irrigated section, from the high mountain valleys to the 
seacoast and from the cold mountain country to the burn- 
ing sands of the low desert, alfalfa thrives and yields 
heavily. It is an excellent preparatory crop for infertile 
or new land. In cases without number it has been found 
that lands on which grain would not at first grow would 
support alfalfa, and that, after some years in this crop, 
the lands would produce grains or any other crop. It is 
a host for nitrogen-gathering forms of life and, therefore, 
increases the fertility of the soil. It is a most palatable 
food for all domestic animals, which thrive upon it. Its 
tonnage is large, averaging about five tons to the acre. It 
is reported that in Arizona and similar districts, excep- 
tional yields of seven tons or more are obtained. With 
proper tillage, an alfalfa field lasts long. Even with the 
improper tillage given the early alfalfa fields of the West, 
there are fields, forty to fifty years old, that are still 
yielding large harvests. When the alfalfa field is disked or 
harrowed annually, it should continue for generations to 
produce undiminished yields. 

Alfalfa requires abundant sunshine, and prefers a high 
summer temperature. It does best on rich, deep, well- 
drained soil. Hardpan or ground water near the surface 
is undesirable, as it tends to prevent the descent of the 
tap-root. Especially is such interference objectionable 



268 IRRIGATION PRACTICE 

when it comes after the plant has developed roots deeply 
in the soil. It is not an ideal dry-farm crop except where 
the ground water is within reach, so that the roots may 
draw water from below. It is essentially an irrigated crop, 
and thrives best where the conditions of soil, tempera- 
ture, relative humidity and sunshine are of an arid 
character. 

There is nothing unusual in the preparation of land 
for alfalfa. It requires a smooth surface preferably with 
a slope of from 10 to 20 feet to the mile. It should be 
sown in drill rows on land well stored with water. It is 
difficult to obtain a stand on raw land. Oats may be sown 
with it as a nurse crop. During the first two years of its 
life it needs careful culture. By that time it is well estab- 
lished and can then receive the regular treatment given 
the matured alfalfa fields. Water should then be kept 
off the land until it is actually needed, so that the plant 
roots may be trained to strike deeply. 

166. Cultivation of alfalfa. — Cultivation of alfalfa 
fields to prevent the evaporation of water is very possible. 
Each fall the alfalfa field is gone over with a disk or a 
harrow, which loosens the top soil to prevent evaporation, 
and, at the same time, leaves the soil so that it may easily 
absorb water and be acted on by atmospheric agencies. 
Meanwhile, the thoroughness with which the older plant 
shades the ground tends greatly to diminish evaporation. 

It is a very common practice, after the last cutting, 
to turn cattle and horses into the alfalfa field, to make use 
of the late growth. When pastures are scarce, and hay 
not abundant, this may be justifiable, but, considering 
the effect upon the field, it is of doubtful value. The 
tramping of the animals makes the soil hard and if there 
are fall rains, the top soil may become puddled and thus 



ALFALFA, FORAGE CROPS AND PASTURES 269 

the alfalfa seriously injured. If such pasturing is not fol- 
lowed by disking, there may be a great diminution in the 
value of the field. Occasionally, stock is turned into the 
field after each cutting. The practice must be wholly 
abandoned. It is also important that stock be kept off the 
field soon after an irrigation. The top soil of alfalfa, as of 
the grains, must be kept in an ideal condition for plant- 
growth. 

167. Method of irrigating alfalfa. — Water may be 
applied to the alfalfa field either by flooding or furrowing. 
If water is abundant, flooding is generally the method 
employed. Check or border irrigation has been used on a 
large scale with alfalfa fields. 

The border method uses sections of the field, about 15 
feet wide, of varying width up to 900 feet long. The bor- 
der levees are about 7 feet wide and 1 foot high, and 
covered with alfalfa. Water is run down in a large sheet 
between these levees. The check method completely 
incloses large fields of alfalfa with levees, into which the 
water is run until it covers the whole field to a certain 
depth. In the inter-mountain region, on the smaller 
fields, where the flooding method is followed, water is 
applied by the field-ditch method. From the supply 
ditch, a transverse ditch is run to the field, from which 
the water is spread over the soil by means of small field 
furrows that do not interfere materially with the plant 
or its harvesting. 

Recently the furrow method promises to displace the 
flooding method for irrigating lucern fields. Where the 
soil tends to run together, or where it bakes hard after 
irrigation, the furrow method is especially employed. 
Where the supply of water is limited, it has been found 
advisable also to employ the furrow method. In furrowing, 



270 



IRRIGATION PRACTICE 



the land, immediately after seeding, is "laid off," ''marked" 
or furrowed. The furrows thus made become permanent, 
and last usually as long as the field is used. They may 
become partly filled from year to year with the sediment 
carried by irrigation water, but this is removed by the 
annual cleaning. The method of applying water by fur- 
rows is the same for alfalfa as for other crops. (Fig. 67.) 




Fig. 67. Plan of irrigating an alfalfa field in Colorado. 

Perhaps 5 per cent of the total irrigated area of alfalfa 
is sub-irrigated by natural means, as already explained. 

168. Time to irrigate alfalfa. — If the fall and winter 
rainfall is insufficient to saturate the soil, fall or winter 
irrigation of alfalfa, especially if the winters are mild and 
open, has been found quite satisfactory. It is imperative, 
however, that water applied to alfalfa in the fall or winter 
be made to soak into the soil, for if water stands on the 
soil, in winter, the crop will probably be injured. Water 
should not be applied in the fall until some time after 



ALFALFA, FORAGE CROPS AND PASTURES 271 

the last harvest, when the plants are dormant. Open, 
dry winters are not conducive to good alfalfa yields. A 
soil of low water content in winter is not so satisfactory for 
alfalfa as one that is near field saturation. However, too 
much water is equally harmful, and may cause winter- 
killing. Free water, found in the upper foot or two of the 
soil, freezes in seasons of high cold, and serious injury 
is done the plants. The alternate freezing and thawing 
of some winters is even more injurious to the crop. If 







| 








i 




| 








% 














%,&/•, 




hfe 


r- 


\ 


>f ShjSJ 












J^iljSBFfl 










\ iDwa 


m *♦ 













Fig. 68. Temporary county fair building constructed of baled alfalfa hay. In a 

pioneer section. 

water is allowed to form ice over the surface, the alfalfa 
plants are fatally injured. The soil should not be too wet 
in the spring, for the low temperature of the soil induced 
by the presence of much water will tend to retard the 
early and important spring growth. 

After the spring growth has begun, the first irrigation 
should be postponed for some weeks, although it is not so 
important to do this with alfalfa as with the annual crops 
that are irrigated late in order to drive their root-systems 
downward. Where wheat is planted in April, the first 



ALFALFA, FORAGE CROPS AND PASTURES 273 

irrigation of lucern usually comes the first or second week 
in June and occasionally as late as the third or fourth week 
in June. Little water in the soil at the time of first growth 
makes it necessary to apply water even earlier. 

It is sufficient, under conditions of deep soil and moder- 
ate evaporation, to give the crop one irrigation for each 
cutting; two or even three light irrigations for each cut- 
ting are not objectionable.* The best present practice is 
to apply water a few days before cutting and again soon 
after cutting — nearly two irrigations for each cutting. 

If one irrigation for each cutting is used, it is always a 
question whether to apply it before or after cutting. If 
water is applied just before the cutting of alfalfa, when the 
land is covered with a heavy growth, there is more trouble 
to cover the land properly with water. On the other 
hand, the water becomes well distributed throughout 
the soil in time to serve the second cutting to the best 
advantage. If the water is applied immediately after 
cutting, there is less trouble in applying it to the clean 
field, but it will take longer time before the plant can make 
as good use of the water as it could if it were already dis- 
tributed throughout the soil. In the Utah work, no appre- 
ciable difference in total seasonal yield was found whether 
the irrigation was applied just before or just after cutting. 
Heavy soils bake more readily if water is applied after 
cutting. 

Bark has determined the time at which alfalfa is irri- 
gated by a large number of Idaho farmers and the per- 
centage of the season's irrigation applied each month. 
The following table shows some of the results: 

Per cent Per cent 

April 1.28 July 30.00 

May 20.90 August 23.75 

June 16.95 September 4.42 

R 



274 



IRRIGATION PRACTICE 



It may be observed that 1.28 per cent of the total 
quantity applied during the seaon, was added in April. 
That undoubtedly was due to the lack of water in the soil 
at that time. The May irrigation, likewise, was doubt- 
lessly applied to lands not well saturated with moisture 
in the spring. The bulk of the irrigation came in July 
and August, during the time of the second and third 
cuttings. 

169. Quantity of water for alfalfa. — The growing sea- 
son for alfalfa is longer than for the small grains, but to 
offset this it uses less water for each pound of dry matter. 
Nevertheless, the heavier acre-yield of alfalfa makes 
necessary more irrigation for alfalfa than for the cereals. 
The law connecting yield of alfalfa with the quantity of 
water used is the same as that developed for other crops. 
In the following table are given the results of experiments 
on the water requirements of alfalfa conducted by Fortier 
in Montana: 

Yields of Cured Alfalfa Hay with Varying Quantities of 

Irrigation Water 



Inches of irrigation 
water supplied 


Pounds per acre 


Pounds per inch 
of water 


6 


9,220 


1,537 


12 


8,840 


737 


18 


7,500 


416 


24 


12,700 


529 


30 


14,400 


480 


36 


15,360 


426 



The depth of irrigation water varied from 6 to 36 
inches; the total yield of well-cured alfalfa hay, from 
9,000 to 15,000 pounds. As shown in the third column of 
the table, the yield did not keep pace with the increase 



ALFALFA, FORAGE CROPS AND PASTURES 275 

in the irrigation water for the harvest of cured alfalfa hay, 
for each inch of irrigation water fell from 1,500 pounds 
when 6 inches of water were used, to 400 pounds when 36 
inches of water were used. The maximum yield did not 
coincide with the economic yield. The results obtained 
by Fortier have been corroborated by the Utah Sta- 
tion. Some of the data obtained are found in the follow- 
ing table: 

Yields of Cured Alfalfa Hay with Varying Quantities of 

Irrigation Water 



Inches of irrigation 
water supplied 


Pounds per acre 


Pounds per inch 
of water 


10 


9,884 


988 


15 


7,546 


503 


20 


9,097 


455 


25 


9,354 


374 


30 


8,840 


295 


50 


10,813 


216 



The irrigation water applied was increased from 10 to 
50 inches, and the yield of cured alfalfa hay increased 
from 9,800 to 10,800 pounds. That is, the yield of cured 
alfalfa for each inch of water fell from 988 pounds to 216 
pounds as the irrigation water was increased five-fold. 
Bark, working in Idaho, found the same law to hold. 
(Fig. 70.) 

While alfalfa does not respond proportionally to the 
application of large quantities of water, yet it can endure 
fairly large irrigations, providing the soil is fertile and not 
too heavy. In water-logged soils, the yield of alfalfa is 
invariably lessened. Alfalfa, not properly cared for by 
harrowing or disking, does not respond well in its yield to 
the water used. This is particularly important in districts 



276 

12000 



CO 900O 

1 

&0OOO 

Si 

f? 



IRRIGATION PRACTICE 



jfLfaLfa, 




Fig. 70. Yield vs. water (alfalfa). 



in m 
mill 

MINI 




the irrigation water of which deposits much silt over 
the soil. 

A small quantity of water will give a fair yield of alfalfa 
hay; good returns are obtained with 12 to 18 or even 24 
inches of water. In general, on alfalfa fields, about one 
and one-half times as much water may be safely used as is 
given to corn and the small grains. On deep soils, alfalfa 



ALFALFA, FORAGE CROPS AND PASTURES 277 

will take more water and give good returns. The abun- 
dance of water must always be considered in determining 
the water to be used on alfalfa fields, for it will determine 
whether the acre yield or the acre-inch yield is of first 
importance. Fortier's results show that 30 acre-inches, 
used on one acre, produce about 14,400 pounds of alfalfa 
hay; on five acres, about 64,100 pounds. It is probably 
safe to say that, on the fertile soils of the West, not more 
than 18 inches of water need be applied to alfalfa, provid- 
ing the crop is given good cultivation. On soils that are 
infertile, shallow, very sandy or underlaid by hardpan, 
more can probably be well used. This depth of water 
refers to districts which receive an annual rainfall of 12 to 
15 inches. Where less rain falls, more water must probably 
be added in irrigation; where more, less need be applied. 

The irrigation season for alfalfa covers approximately 
120 days — June to September, inclusive. During this 
period one second-foot will cover 240 acres to a depth of 
12 inches; 150 acres to a depth of 18 inches; 120 acres 
to a depth of 24 inches. The best managed irrigation 
systems have a duty of water for alfalfa of about 150 
acres, which is increasing. 

Irrigated alfalfa hay is of high quality. The quantity 
of water used in producing alfalfa determines, in a large 
measure, the quality of the hay. The more water used, the 
more woody the hay becomes, and the less valuable, 
therefore, for feeding purposes. The less water used, the 
richer the hay becomes, per pound, in the blood- and 
muscle-forming elements. All in all, as with other crops 
so with alfalfa — it must be grown with a moderate quan- 
tity of water. 

170. Alfalfa seed. — The present large demand for al- 
falfa seed is likely to continue as long as new lands are being 



278 IRRIGATION PRACTICE 

brought under irrigation. The conditions determining the 
production of alfalfa seed are not well understood, but the 
chief secret seems to be the use of little water. The first 
cutting is harvested as usual for hay; the second cutting 
is allowed to go to seed with little irrigation — none if the 
first cutting has been well irrigated; after the harvest, 
water is added to obtain, if possible, a small third crop. 
The use of much water diminishes the yield of seed, and 
also retards the production of the seed until too late in 
the fall. Morgan, working in Utah, obtained the highest 
yield of seed when about 8 inches were used. Either less 
or more resulted in smaller yields of seed. In other locali- 
ties, some other quantity might be found to be best, but 
it is never large. Another method of producing alfalfa 
seed is to clip the first growth of alfalfa about the time 
of the first irrigation, or a little earlier, and then to allow 
the first crop to go to seed. By many, this is held to be 
by far the most successful method of producing alfalfa 
seed. The whole matter needs much careful experimental 
study before definite rules can be laid down. 

171. Hay-making crops. — The standard hay-making 
crops may all be produced under irrigation. With the 
growth of irrigation there will be an increasing demand 
for a variety of hay-making crops. While nearly all hay- 
making crops will thrive under irrigation, they do so with 
varying degrees of success, depending upon their adap- 
tability to the soil and climatic conditions of the irrigated 
region. Usually, some years of adaptation precede the 
best results from any crop introduced into the irrigated 
region. 

The Utah work included studies of timothy, orchard- 
grass, brome-grass, and Italian rye-grass, all of which 
are typical hay-making crops. These were planted as 



ALFALFA, FORAGE CROPS AND PASTURES 279 

usual, took root and grew well. Plenty of water was added 
in the spring to cause an early start and to imitate a cool, 
moist spring; after which water was held off for several 
weeks, until near the time of cutting. Any of the well- 
established methods of applying water may be used. From 
5 to 100 inches were used in the experiments. In every 
case there was a smaller yield with 100 inches than with 
5 inches. In some cases, smaller yields were obtained 
with 10 to 15 inches than with 5 inches. The evidence of 
the available experimental work is that these grasses 
tolerate only small quantities of water. The following 
table shows some of the results obtained in the Utah work : 



Yield in Pounds per Acre 



Irrigation 
water used 


Timothy 


Orchard-grass 


Brome-grass 


Italian 


in acre-inches 








rye-grass 


5.0 




2,526 






7.5 


3,982 


. 


4,480 


2,357 


10.0 


. . 


2,829 


4.957 


. . 


15.0 


3,844 


2,685 


, . 


2,218 


30.0 


6,054 


. . 


3,821 


. . 


40.0 


. . 


4,042 


9 . 


. . 


45.0 


m . 




m m 


# # 


60.0 


8,406 


5,270 


4,757 


3,201 


100.0 


2,214 


1,192 


3,068 


2,357 



Since the roots of these plants do not penetrate the 
soil deeply, the frequent application of water may be 
justified, but the total quantity need not be great. Timo- 
thy appears to endure much water better than the other 
crops. One crop only is obtained from these grasses, and 
they are, therefore, much like the small grains in their 
water requirements. Ordinarily it is sufficient to give 
these crops one good irrigation before cutting. From 5 to 
10 inches of water should be sufficient to produce the one 



280 



IRRIGATION PRACTICE 



crop of hay. On infertile or sandy soils from 10 to 15 
inches should be ample. Where the aftermath is pastured, 
the field may be irrigated lightly once or twice during the 
hot months of July and August, when good pasturage 
results until late in the fall. 

These and other grasses, especially the native grasses, 
are often grown on the large ranches of the West. One 
crop is ordinarily harvested and the aftermath pastured. 
As early as possible in the spring, these fields are covered 




Fig. 71. Flooding pasture land. 

with immense quantities of water, which often stand for 
days, 1 to 2 feet deep. It is believed that under such con- 
ditions the frost is taken out of the soil, and a larger 
quantity of hay is obtained. The experiments at our ser- 
vice indicate that all hay crops are injured by an excess 
of water, and that the best yields are obtained only by 
moderate irrigations. The immoderate use of water on 
such ranches should be discontinued, for it is an absolutely 
senseless practice. The hay-making grasses, whether 
tame or wild, should not be given too much water if large 
yields are desired. 



ALFALFA, FORAGE CROPS AND PASTURES 281 

172. Red clover. — Red clover, and the other clovers, 
should be irrigated much as is the first cutting of alfalfa, 
or the grasses above discussed. All the standard forage 
crops are subject to the laws already laid down. It is 
probable that from 12 to 15 inches would meet amply 
the requirements of practically any one of the standard 
hay crops. The longer the growing period of the crop the 
larger will be the necessary quantity of water. When 




Fig. 72. Irrigating young alfalfa. 

vetches and peas are grown for hay they are to be treated 
as indicated for peas in Chapter XV. 

173. Pastures and meadows. — Many natural meadows 
are supplied with water from below. In fact, in the irri- 
gated section, the term meadow is generally applied to 
natural pastures where no irrigation is needed. These 
sometimes become dry in the summer, and must then be 
irrigated. The time and quantity of application depend 
entirely upon the prevailing conditions. No rules can be 
laid down. 



282 IRRIGATION PRACTICE 

The chief pastures of the irrigated region are those that 
are irrigated throughout the season; and these pastures 
are the finest known to agriculture. They may be kept 
green and luxuriant throughout the season, and, there- 
fore, will support many times the head of live-stock pos- 
sible on unirrigated pastures of humid regions. As live- 
stock husbandry develops under irrigation, pastures will 
rapidly increase. 

There is as yet no unity in the practice of selecting 
mixtures of grasses for irrigated pastures. All the stand- 
ard pasture grasses are used in a variety of combinations 
under irrigation. Thus, in various combinations accord- 
ing to soil, climate and individual views, the following 
are used on the irrigated pastures of the West: Kentucky 
blue-grass, perennial rye-grass, meadow fescue, red clover, 
red-top, orchard-grass, white clover, alfalfa, meadow oat- 
grass, brome-grass, Rhode Island bent, timothy, alsike, 
and many of the native grasses, which, as they become 
better known, will become important factors in the 
reclamation of the West. The proper mixture, culture 
and irrigation of these plants will give a constant, free, 
luxuriant pasturage that should bring dairying and 
related branches of live-stock husbandry to their highest 
possible development. 

All pastures should receive fairly heavy irrigations in 
the spring, and if they are used throughout the season 
should be irrigated during the whole summer. Pastures 
that are well established on deep soils, should not be irri- 
gated, after the irrigation season begins, oftener than every 
two weeks, and then to a depth of 3 to 4 inches. If the pas- 
tures are on gravelly or shallow lands, water must be 
applied perhaps as often as once a week, but in such cases 
less water should be applied at each irrigation. 



ALFALFA, FORAGE CROPS AND PASTURES 283 

The irrigation season for pastures is approximately 
the same as for corn or potatoes. The largest need for 
water is in July and August, when the hot weather causes 
the most rapid evaporation. Irrigated pastures must not 
be allowed to become very dry, for it is difficult for the 
pasture to recover in a season from a set-back due to a 
period of extreme dryness. On the other hand, the fal- 
lacy of over-irrigation should be avoided. Pastures do 
not need much more water than do the hay crops. The 
long growing season, the shallow root-system and the 
variety of plants in the pasturage mixture, make it difficult 
to foretell the best quantity of water for pastures. With 
our present knowledge, however, it is safe to say that 
from 12 to 24 inches of water should be ample to main- 



i.' 

Km & <i *^V fL* WnSm 


i - ■ ■ *"- 



Fig. 73. Irrigated cane in Kansas. 



284 IRRIGATION PRACTICE 

tain any well-planted pasture in a luxuriant condition 
throughout the season. This is a wide limit, and it is 
probable that the best quantity lies near 18 inches. 

Irrigated pastures should not be grazed in early spring 
or immediately after an irrigation, when the soil is soft, 
because the plants may then be materially injured. 
Meadows and pastures should be frequently disked or 
harrowed, so that the top soil may be kept in a somewhat 
loose condition. Such treatment will diminish the quantity 
of water required throughout the season. Under the 
most favorable conditions, the constant tramping of 
animals on pastures will compact the top soil and thereby 
increase evaporation, decrease the rate of water penetra- 
tion and increase the quantity of water required for the 
growth of the plants. The key to pasture maintenance 
seems to be the relatively frequent applications of small 
quantities of water to prevent any period of excessive 
dryness. 

REFERENCES 

Bark, Don H. Duty of Water; Investigations (1910-12). Ninth 
Biennial Report, State Engineer of Idaho (1912). 

Coburn, F. D. The Book of Alfalfa. Orange Judd Company 
(1902). 

Evans, M. W. Timothy Production on Irrigated Lands in the 
Northwestern States. United States Department of Agricul- 
ture, Farmers' Bulletin No. 502 (1912). 

Fortier, Samuel. Irrigation of Alfalfa. United States Department 
of Agriculture, Farmers' Bulletin No. 375 (1909). 

McLaughlin, W. W., and Morgan, E. R. Report on Irrigation 
Investigations during 1905-06. Utah Experiment Station, 
Bulletin No. 99 (1906). 

Olin, W. H. American Irrigation-Farming. A. C. McClurg Com- 
pany (1913)/ 



ALFALFA, FORAGE CROPS AND PASTURES 285 

Teele, R. P. Review of Ten Years of Irrigation Investigations. 
United States Department of Agriculture/ Office of Experiment 
Stations, Annual Report for 1908 (separate). 

Welch, J. S. Irrigation Practice. Idaho Experiment Station, 
Bulletin No. 74 (1914). 

Westgate, J. M., McKee, Roland, and Evans, M. W. Alfalfa 
Seed-Production. United States Department of Agriculture, 
Farmers' Bulletin No. 495 (1912). 

Widtsoe, J. A., and Merrill, L. A. The Yields of Crops with Dif- 
ferent Quantities of Irrigation Water. Utah Experiment Sta- 
tion, Bulletin No. 117 (1912). 

Widtsoe, J. A., and Merrill, L. A. Methods for Increasing the 
Crop-producing Power of Irrigation Water. Utah Experiment 
Station, Bulletin No. 118 (1912). 

Wilcox, Lucius M. Irrigation Farming. Orange Judd Company 
(1902). 

Wing, Jos. E. Alfalfa Farming in America. Sanders Publishing 
Company (1909). 



CHAPTER XV 

SUGAR BEETS, POTATOES AND 
MISCELLANEOUS CROPS 

Among the most satisfactory irrigated crops are those 
that pass through some process of manufacture before 
they are placed upon the market. Thus, sugar beets 
reach the consumer as sugar; potatoes, often as starch; 
hay as butter or cheese; fiber crops as twine and rope; oil 
crops as oil, and so on. It must be the great endeavor of 
irrigation agriculture, the initial cost of which is often 
larger than that of humid agriculture, to foster crops that 
may be manufactured. Not only do such crops make it 
possible to maintain more easily the fertility of the soil, but 
they represent steady prices and ready markets. 

174. Sugar beets. — The most typical irrigated crop, 
in view of the development of irrigated commonwealths, 
is the sugar beet. All fairly fertile soils may produce 
sugar beets, providing proper methods of culture and 
irrigation are followed. Sugar beets endure alkali 
better than most crops; they yield fairly well even on 
the shallow, sandy or gravelly soils of the mesas. A clay 
loam of good depth is preferable, if it can be obtained. 
Sugar beets respond well to an arid climate and to dry 
summers. 

Sugar beets require careful soil preparation and an 
even sowing and thinning. It is a common practice, 
apparently to assure uniform and rapid germination, to 
roll the soil after the seed has been placed in the ground. 

(286) 



288 



IRRIGATION PRACTICE 



Rolling of the top soil, however, invariably causes a loss 
of soil moisture, and it may be necessary for the beet- 
growing sections to revise their practice in this particular. 
If the soil is rolled, it should be followed immediately, if 
possible, with a harrow to stir the top soil. Sugar beets 
are always planted in rows, to permit of easy cultivation 










°Jr' _> . r w' 



Fig. 75. Unloading sugar beets in factory bins. 

between the rows, which is usually done by horse power. 
Cultivation, an essential factor in sugar-beet-growing 
under irrigation, should be practised after each irrigation 
and two to four times between successive irrigations. As 
with other inter-tilled crops, the more frequent and 
thorough the cultivation of the soil, the smaller the quan- 
tity of water required for the production of the crop, and 
the better the quality of the crop. 



SUGAR BEETS, POTATOES, ETC 289 

175. Method of irrigating sugar beets. — The careful 
leveling of the land before sowing adapts sugar beet 
fields to the furrow method of irrigation, although either 
furrowing or flooding may be practised. In earlier days, 
the field ditch method of flooding was used for sugar beet 
fields, and in California, today, many of the beet fields are 
irrigated by the border method of flooding. By the flood- 
ing method, serious injury often results from contact 
between the water and the heavy leaves of the beets. 
Especially on hot days, immediately after an irrigation, is 
a kind of sun-scald induced by too much water on the 
ground near the leaves. Once a crop is set back by such 
sun-scald, it recovers slowly. This trouble is largely 
obviated when the furrow method is employed. All in 
all, the furrow method of irrigation gives the most satis- 
factory results in sugar beet culture and is rapidly dis- 
placing the flooding method. The rows are usually about 
3 feet apart, with the furrows half way between. If the 
soil sub-irrigates easily, the furrow may come between 
every other row. Cross ditches are run at the head of the 
field and every 300 to 500 feet to intercept the water from 
above and to supply the adjoining lower section of the 
field. The quantity of water allowed to run down each 
furrow is small, except when a high head is used for the 
special purpose of covering the field quickly. As with 
corn and the other crops already discussed, it is well not 
to make the rows too long. The ideal of every method of 
irrigation is to distribute the water equally over the whole 
field, so that each plant may receive the same quantity of 
water. This is best accomplished by the furrow method 
of irrigation. 

One of the main difficulties in all furrow irrigation is 
to secure a uniform application of water in the different 
s i 



290 IRRIGATION PRACTICE 

furrows. Many soils "wash" easily, and if connections 
are made with the main supply ditch by simply hoeing out 
a small opening, the water is likely to make the opening 
larger, or by shifting, even to close it, so that the water 
does not for any length of time flow down the furrows as 
intended by the irrigator. In many sugar beet fields and 
orchards, small boxes, made of lath or lath-like boards, 
about an inch square on the ends and 24 to 30 inches long, 
are placed at the head of each furrow-opening, connecting 
the furrow with the head supply ditch, and establishing a 
permanent opening into each furrow, not easily disturbed 
by the moving water. These boxes can be placed a little 
higher or lower with very little effort, so that practically 
the same quantity of water may enter each furrow. With 
devices of this kind it is possible for one man to irrigate 
a very large tract in a very short time. 

Roeding determined the relative yields obtained when 
the same quantity of water was applied to a sugar beet 
field by the open furrow and by the lath-box furrow. When 
lath boxes were used to carry the water into the furrows, 
thus providing a slower and more regulated flow, 16.47 
tons of beets were produced to the acre. When the furrow 
opened directly through the earth into the supply ditch, 
making it difficult to control the quantity and even dis- 
tribution of water, the yield of beets per acre fell to 13.72 
tons. This emphasizes the value of an even distribution 
of water over the sugar beet field, and naturally over 
fields of any other crop. The sub-irrigation of sugar beets 
has been found feasible only in a few localities where the 
lands are naturally sub-irrigated. It has not been found 
profitable to install subterranean channels for water, with 
outlets at various intervals, for irrigation purposes. 

176. Time to irrigate sugar beets. — The beet crop is 



SUGAR BEETS, POTATOES, ETC. 291 

greatly benefited by winter irrigation. The land is bare 
in fall and winter so that irrigation cannot injure the 
crop, and the soil is invariably benefited by late irriga- 
tions, providing the natural rainfall of fall, winter and 
spring is not sufficient to saturate the soil to the full 
depth of root-action. Where the winters are dry, 
winter irrigation of sugar beets has been found very 
profitable. 

There should be water enough in the soil in the spring 
to germinate the plants without further irrigation. If, at 
the time of seeding, there is not sufficient water in the 
soil to insure rapid and complete germination, it becomes 
necessary to apply water just before or after seeding. 
Whether such irrigation for germination should be before 
or after seeding is still undecided. In some sections the 
general practice is to irrigate before seeding; in other 
sections, excellent results are obtained by irrigations 
after seediug. 

The first irrigation should be postponed as long as 
possible after planting, as early irrigations bring the 
root-system to the surface and produce a turnip-shaped 
beet with a heavy growth of leaves, which in turn means a 
large, wasteful use of water later in the season. The sugar 
beet makes its most rapid growth after late spring and 
early summer, so that the crop has little need of water 
early in the season. Evaporation is great from the large 
leaf surface, and the leaves occasionally wilt slightly 
toward the end of a hot day. This may occur on soils well 
supplied with water, and implies only that water cannot 
be drawn from the soil as rapidly as it is evaporated from 
the leaves. If, in the morning, there is no evidence of 
wilting, no fear need be had about the condition of the 
crop, and the next irrigation need not be hurried along; 



292 IRRIGATION PRACTICE 

but, if the beets are wilted in the morning, it is a fairly 
sure sign that irrigation is necessary. 

On the deep, fertile soils of the West two to four irri- 
gations should be sufficient for the season. On porous, 
gravelly soils, more water will be necessary. Many of the 
sugar factories advise two irrigations; few advise more 
than three. In liberal practice, three to five irrigations 
should be ample. The final irrigation should occur at 
least four to six weeks before harvest; that is, from Sep- 
tember 1 to September 15, so that the beets may have 
ample time to ripen in the cool weather of fall, and be 
ready for the factory. Water applied late causes late 
growth, with a decided fall in the sugar content, and often 
in the yield. The great length of the growing season makes 
it probably better to apply a small total quantity of water 
in several irrigations than in one. Many irrigations tend 
to give an increase in the yield; but more than four or 
five seldom pay in added yield for the increased cost of 
irrigation. Where the annual rainfall is from 12 to 15 
inches, most of which falls in winter and early spring, 
there is little or no need of irrigation in June. In July, when 
the growth is rapid, two irrigations; in August, not more 
than two, and in September, at the most one irrigation 
should be applied. The Utah work indicates that, of the 
total quantity of water to be applied throughout a sea- 
son, about 45 per cent should be added in July; 35 per 
cent in August, and about 20 per cent in June and Sep- 
tember. A small total quantity during the season elimi- 
nates irrigations in June and September. Clay loams 
should not be irrigated oftener than every two weeks. The 
number of irrigations in a season depends, after all, upon 
the total quantity to be used. With a heavy annual rain- 
fall, little irrigation, therefore few applications; with lighi} 



SUGAR BEETS, POTATOES, ETC. 



293 



rainfall, more irrigation and more frequent applications. 
Beets, like all long-season crops, require water during 
the hot months of rapid growth, when the water runs low. 
Under reservoir conditions, this makes little difference, 
since water can be sent to the farms at the time of great- 
est need; but, where canals are taken directly from the 
rivers, it is often difficult to supply a large acreage of long- 
season crops with all the water needed in July and August. 




Fig. 76. Irrigating potatoes. 

177. Quantity of water for beets. — Whether 23^, 5 or 
7J^2 inches of water are to be applied at each irrigation, 
depends on climatic, soil and cultural conditions. The 
plant should be allowed to drain thoroughly the water 
from the soil. Then, a quantity of water should be added to 
bring the soil moisture up to the full field capacity. 
Ordinarily, 4 to 6 inches are used at each irrigation, but 
in the hot summer months of low water, 2 to 3 inches only 
are applied. It is inadvisable at any time to apply in 
one irrigation very large quantities, as for instance, 1 foot. 



294 



IRRIGATION PRACTICE 



The sugar beet, like the other crops hitherto studied, 
is subject to the law that the increased yield due to the 
increase of irrigation is not proportional to the added 
quantity of water. Roeding found, as shown in the fol- 
lowing table, that during the season of 1905-06, on a 
clayey loam of good depth, as the water was increased 
from 6 to 18 inches, or three-fold, the yield increased only 
from approximately ten tons to nearly thirteen tons to 
the acre. The Utah results, as also shown in the following 
table, are practically the same. 

Yields of Sugar Beets with Varying Quantities of 
Irrigation Water 



Inches of irrigation 
water applied 


Tons per acre 


Tons per inch 
of water 


Roeding' s results — 






6.1 


9.7 


1.59 


10.0 


10.8 


1.08 


16.8 


11.8 


0.70 


18.4 


12.8 


0.70 


Utah results — 






5.0 


13.8 


2.76 


10.0 


18.6 


1.86 


15.0 


19.5 


1.30 


20.0 


21.3 


1.06 


30.0 


20.8 


0.69 


50.0 


24.5 


0.49 



Water was applied from 5 inches to 50 inches, or ten- 
fold. The yield under this treatment increased from 13.8 
tons to 24.5 tons, or not quite double. Within these 
limits the yield per inch of irrigation water fell from 2.76 
to 0.49 tons of sugar beets. (Fig. 77.) 

By understanding this law, the possibility of 30 acre- 
inches may well be illustrated. If 30 acre-inches are made 
to cover 1 acre, the yield is 20.82 tons of sugar beets; 2 



SUGAR BEETS, POTATOES, ETC. 



295 



acres, 38.90 tons; 3 acres, 55.89 tons; 4 acres, 64.89 tons; 
6 acres, 82.68 tons. Whether, in consideration of the 
scarcity of water and the abundance of land, it would be 
preferable to grow twenty-one tons of sugar beets on 1 
acre with 30 inches, or eighty-three tons on 6 acres, with 
the same quantity of water, is a thing that each community 
must determine for itself. However, it is questionable if 
sugar beets should receive during any season more than 
18 inches of water, representing three heavy irrigations, 



30 



<0 



3" 






Stu/CLr JBeets 



Hill 



mi i 



I 



^60 






Fig. 77. Yield vs. water (sugar beets? 



296 IRRIGATION PRACTICE 

or four lighter irrigations, or six light irrigations. Within 
existing practice, sugar beets receive from 15 to 24 inches 
of water, according to the prevailing water conditions, 
except in the newer districts where water is abundant, 
when even more is used. The development of more rational 
methods will reduce the quantity now used. 

The irrigation season for sugar beets seldom exceeds 
ninety days. If a depth of 15 inches of water is applied 
during this season, a second-foot of water will have a 
duty of 144 acres; if 18 inches are applied, a duty of 120 
acres, and if 24 inches are applied, a duty of 90 acres. 
The present practice makes the duty of water for sugar 
beets about 150 acres, with a rapid upward tendency. 

As explained in Chapter XI, the percentages of sucrose 
and purity are highest when medium quantities of water 
are used in sugar beet production. The quality of sugar 
beets is especially improved when water is withheld 
several weeks before harvest. The ripening and increase 
in sugar and purity go on until very late in the fall. Water 
is often applied late, in the hope that the yield may be 
increased. This seldom occurs, and when an increased 
yield is obtained, it seldom pays for the labor of irriga- 
tion; moreover, it causes a decided loss to the sugar fac- 
tory, which depends upon the sugar content for its profit- 
able operation. Sugar beets bought on the basis of sugar 
are not subjected to late irrigations. 

The shape of the sugar beet is materially improved 
when moderate quantities of water are used. An early 
irrigation produces turnip-shaped beets, and late or heavy 
irrigations produce forked or irregular beets. 

178. Carrots. — Carrots are grown practically as are 
sugar beets, though less attention is given to quality and 
more to the total acre yield. Irrigation studies of this 



SUGAR BEETS, POTATOES, ETC. 



297 



crop show that carrots are subject to the laws that prevail 
with other crops. As shown in the following table, when 
the water applied increased from 3% inches to 60 inches, 
the total yield increased only from 7.3 tons to 34.2 tons 
per acre; the yield per inch of irrigation water diminished 
from 4.35 tons to 0.57. However, carrots seemed to 
respond more readily than did sugar beets to large quan- 
tities of water. The total quantity of water to be used 
throughout the season is about the same as that recom- 
mended for sugar beets. 



Total Yield of Carrots with Varying Quantities of 
Irrigation Water 



Inches of irrigation 
water applied 


Total yield in tons 


Total yield 
per inch of water 


3.75 


17.3 


4.35 


7.50 


16.6 


2.22 


15.00 


24.8 


1.65 


25.00 


23.4 


0.94 


35.00 


28.5 


0.82 


60.00 


34.2 


0.57 



179. Other root crops. — Root crops are becoming of 
greater importance as the live-stock business increases. 
Turnips, beets, mangels, parsnips, radishes and all similar 
crops, when grown as field crops, may be treated practi- 
cally as sugar beets and carrots. When grown in gardens 
they are sown more closely, and the water requirements 
are somewhat higher. They are always irrigated in fur- 
rows and precautions are taken not to bring water in actual 
contact with the growing plant, especially during hot 
weather. Beets are usually irrigated every two weeks; 
radishes and early spring crops require little total water, 
but most of it very early; turnips get along with little 



298 



IRRIGATION PRACTICE 



water — considerably less than sugar beets. Little exact 
knowledge has been gained concerning the irrigation of 
these crops. Practical experience, however, teaches that 
much water delays the time of ripening; it is usually 
sufficient to irrigate the garden every two or three weeks; 
water should be taken off as soon as ripening should com- 
mence; it is always dangerous to maintain water on these 
crops in the fall; and the total water required is not 
greatly different from that required for sugar beets. 



3ub- lateral 



3 C 

3 c 
3 C 
D C 
3 C 
3 C 
3 C 
31C 




3~C 

3 C 
3 C 
3 C 
3 L 
3 C 
3 C 
3-Z 
3 C 



Fig. 78. Plan of potato irrigation. 

180. Potatoes. — Potatoes are one of the important 
irrigated crops. In its water requirements the potato is 
much like the sugar beet. It is a long-season crop, requir- 
ing thorough cultivation. It is deep-rooted and prefers 
deep soil, and does best on land previously grown to 
alfalfa. 

Potatoes should be irrigated by the furrow method, 
although both furrowing and flooding methods are used. 
Water is usually allowed to run down between all the 



SUGAR BEETS, POTATOES, ETC. 



299 



rows, although on soils with good lateral seepage it may be 
sufficient to irrigate every other row. Occasionally, every 
other row only is irrigated at the first irrigation, and every 
row thereafter. (Figs. 76-79.) 

Potatoes need a good supply of water in the soil at 
planting time. If the soil is too dry, it may be necessary 
to irrigate the crop, which may be accomplished by 




Fig. 79. Irrigating potatoes at Greeley, Colo. 

applying water just before or after planting. Little water 
is needed by potatoes during the first period of growth, 
providing there is a plentiful supply in the soil at the time 
of planting. Potatoes planted about the first of May 
seldom need irrigation before July 1; and from then on 
irrigation should be practised only as the plants need it. 
One of the surest signs of water need is the darkening of 
the foliage. If water, especially cold water, is applied too 



300 



IRRIGATION PRACTICE 



frequently, growth is seriously retarded. It is well to 
secure a good growth early, and to develop early a deep 
root-system that may endure the heat of midsummer. It 
is seldom advisable to irrigate oftener than every two 
weeks, and every three or four weeks frequently gives 
satisfactory results. Irrigation should cease about the 
middle of August, leaving about sixty days for the ripen- 
ing of the potatoes. Potatoes are seriously injured by 
over-irrigation. The first visible effect of too much water 
is a light green color acquired by the leaves. The Utah 
Station conducted experiments on the effect of varying 
quantities of water on the yield of potatoes. Some of the 
results obtained are found in the following table: 



Inches of 

irrigation water 

applied 


Yield in 
bushels 
per acre 


Bushels 

per inch of 

irrigation water 


Percentage of 

marketable 

potatoes 


5.0 


154 


30.8 


74.80 


7.5 


182 


24.3 


74.70 


10.0 


195 


19.5 


77.94 


15.0 


227 


15.1 


82 12 


20.0 


267 


13.4 


80.62 


30.0 


244 


8.1 


79.81 


45.0 


253 


5.6 


79.50 


60.0 


304 


5.1 


76.90 



The total quantity of water used varied from 5 to 60 
inches, or twelvefold. The yield of potatoes increased 
meanwhile from 154 bushels to 304 bushels, or not quite 
double. The yield to the inch of irrigation water fell, as the 
water was increased, from 30.8 bushels to 5.1 bushels or 
about one-sixth. As shown in the last column of the above 
table, the percentage of marketable potatoes in the total 
crop increased, with the increase in water, up to medium 
quantities, after which it fell definitely. Clearly, the law 



SUGAR BEETS, POTATOES, ETC. 301 

connecting yield with irrigation is the same for potatoes 
as for other crops. However, the yield of potatoes is 
more nearly proportional to the water used than are 
sugar beets or the other root crops. This may be due to 
the fact that the potato is an enlarged stem. Following 
the Utah results, when 30 acre-inches were applied to 1 
acre, 195 bushels of potatoes were obtained; when spread 
over 6 acres, 691 bushels were obtained. (Fig. 84.) 

The quality of potatoes is also definitely affected by 
the quantity of water used. Medium quantities produce 
starchy potatoes; if too little or too much water is used, 
the percentage of starch is materially lowered. 

It is probable that the duty of water for potatoes 
should not be greatly different from that for sugar beets. 
From 15 to 24 inches should represent an ample quantity 
of water for the production of a good crop of potatoes, 
wherever the annual rainfall is in the neighborhood of 15 
inches, and where the soils are deep and well cultivated. 
It has been found possible in the arid regions to raise 
large crops of first-class potatoes without irrigation, and it 
is probable that the duty of water for potatoes will be 
greatly increased as fuller knowledge is obtained. 

181. Peas and beans. — Peas and beans are becoming 
important irrigated crops. They are especially valuable 
because, like lucern, they grow well on raw soils that 
are unwilling to yield the ordinary crops when first brought 
under cultivation. Of late years these crops have become 
valuable in the hog and sheep industry. The sheep eat 
the vines and the hogs the seeds. Large quantities of the 
proper varieties of peas are also canned, and in that con- 
dition shipped all over the earth. 

Peas and beans may be grown either as garden or 
field crops. They are characterized by a rather short 



302 



IRRIGATION PRACTICE 



growing season, and in that particular are comparable 
with the small grains and the grasses. They should be 
sown in rows, between which cultivation should be prac- 
tised as long as possible. Large yields may be obtained 
with small quantities of water, providing they are care- 
fully cultivated after each irrigation, and several times 
between successive irrigations. 




Fig. 80. Irrigated field peas. 



The furrow method of irrigation is almost invariably 
used. The furrows are about 3 feet apart, and, to avoid 
sun-scald, so filled that water does not touch the plants. 

These crops should be planted in moist soils, and, if 
the soil is dry, it may be necessary to irrigate them 
either by adding water just before or after seeding. After 
seeding they need little water until the soil becomes some- 
what dry. However, they are rapid growers and water 



SUGAR BEETS, POTATOES, ETC. 



303 



must be applied whenever needed, so that they may 
suffer no set-back because of intense dry spells. Peas and 
beans finish most of their growth in spring and early sum- 
mer, when there is usually an abundance of water. Just 
before and at the time of blooming the largest quantity 
of water is required. When the pods are pretty well 
formed little water is required, and soon afterward 
irrigation may be stopped altogether. In fact, a somewhat 
dry soil, after the pods are well formed, helps in the 
formation of the seed. Peas, which require less water 
than beans, when grown for seed require only one irriga- 
tion; when grown for fodder, two or three irrigations may 
be applied. It is often profitable to grow two crops of 
peas. One is harvested early in July and the other in 
early fall. 

The Wyoming Station has conducted experiments 
on the quantity of water used by peas. Some of the 
results obtained are shown in the following table : 



Total inches of 

irrigation water 

applied 


Total tons of 

forage 

per acre 


Total yield of 

peas per acre. 

Bushels 


Per cent 

of peas 

in forage 


22.92 


4.20 


19.21 


14 


20.09 


2.84 


34.75 


37 


17.73 


1.77 


16.56 


28 


9.13 


1.74 


11.17 


19 


5.02 


1.27 


6.04 


14 


• • 


0.66 


3.00 


14 



The quantity of water used varied from none to 
22.92 inches. The acre yield of forage varied from .66 
tons to 4.20 tons. The total acre yield of peas varied from 
three bushels to nineteen bushels. The percentage of 
peas in the whole crop varied from 14 to 37. The yield 
did not increase so rapidly as the water increased. The 



304 



IRRIGATION PRACTICE 



percentage of seed increased with the water, which is 
distinctly different from the behavior of the grains, in 
which the proportion of seed decreases with an increase 
in water. From 10 to 15 inches of water are probably 
ample for the production of peas or beans under present 
methods. This depth will be decreased as irrigation prac- 
tices are perfected. 



■ ■•* ' ,* 















'•■>.*'),l'j. 






Fig. 81. Irrigated celery. 



SUGAR BEETS, POTATOES, ETC. 



305 




Fig. 82. Irrigated pumpkins. 

182. Fiber crops. — The strength of irrigation agricul- 
ture will increase as the crops grown are related to manu- 
facturing industries. The fiber crops are, therefore, impor- 
tant. Hemp grows exceedingly well under irrigation; and, 
from the irrigated crop, fiber of the highest quality has 
been made. It is always grown in rows and irrigated by 
furrows. Since it attains great growth it requires consider- 
able water. Flax is likewise of easy culture under irriga- 
tion. It must always be irrigated by furrows, since it is 
subject to sun-scald. It requires little water; in fact, it 
has been grown on dry-farms with great success. Cotton 
has been grown under irrigation for more than fifty years, 
and in quantities sufficient to supply a cotton-mill, which 
was established at that time. In more recent days cotton- 
growing has been established successfully in the Imperial 
Valley of California and in southern Arizona. It is irri- 
T 



306 IRRIGATION PRACTICE 

gated by the furrow method. It uses little water. The 
soil should be moist at planting, and the crop usually 
receives but one irrigation after planting. 

183. Hops. — Hops is another valuable crop, which is 
grown to a limited extent under irrigation. In the humid 
hop-growing sections, supplementary irrigation is a very 
common practice. Hops are easily grown, and are irriga- 
ted by either the furrow or the flooding method. Water 
is applied every three or four weeks. The heaviest irriga- 
tions are given as the buds appear. No irrigation is applied 
after August 15, when the crop is about to ripen. 

184. Tomatoes, cantaloupes, etc. — These and similar 
crops do excellently well under irrigation. Tomatoes, 
especially, have become a very important crop as canning 
factories have been established. The plants are set out in 
rows in the usual way, and the water is applied invariably 
by the furrow method. If careful cultivation is applied 
to the irrigated field, the tomato plant does not demand an 
excessively large quantity of water. Too much water 
encourages too great a growth of vines, and interferes 
with ripening. The first irrigation is postponed as long as 
possible after planting, and, when the irrigation season 
begins, three irrigations are usually sufficient for the sea- 
son. Heavy irrigation at the time of ripening tends to 
increase the weight of the crop, and farmers who supply 
the canning factories, therefore, apply at that time large 
quantities of water; so large, indeed, that growth is stopped 
and the ripening fruit is well filled with water. In other 
places, at the time of ripening, water is refused the plant 
entirely, leaving excellent fruit, although the total weight 
is not so great. During picking it is a common practice to 
apply water largely, with the result that the yield is 
increased. The cultivation of tomatoes throughout the 



SUGAR BEETS, POTATOES, ETC. 



307 



season is really as important as the irrigation. The total 
quantity of water required for tomatoes is seldom in 
excess of 18 inches. Occasionally, good crops are pro- 
duced with less water. 

Watermelons, cantaloupe, squash, pumpkin, eggplant 
and similar crops grow well under irrigated conditions. 
Of these crops the cantaloupe is especially important. The 
watermelon needs little water, and practically none after 
it is half grown. Two or three irrigations in a season seem 
to be enough. Cantaloupes require a little more water. 




Fig. 83. Irrigated onions in Arizona. 



308 



IRRIGATION PRACTICE 



After flowering, and during fruiting, more water is required 
than before. Cultivation is the main consideration in 
the culture of both watermelon and cantaloupe. To 
obtain crops of high quality, water should be limited at 
the time of ripening. Pumpkins and squash should be 
irrigated very much as the watermelon. No exact records 
are available, but the evidence points to 10 to 12 inches 
of water as ample for most of these crops. 

185. Cabbage, cauliflower, etc. — These typical gar- 
den crops, sometimes grown as field crops, use fairly 
large quantities of water. The Utah Station has made 
some experiments as to the effect of varying quantities 
of water. Some of the results are shown in the following 
table : 



Yields of Cabbage with Varying Quantities of Irrigation 

Water 



Inches of 

irrigation water 

applied 


Tons per acre 


Tons per acre-inch 
of water 


12.5 


9.2 


.74 


20.0 


9.2 


.46 


25.0 


8.2 


.32 


40.0 


10.2 


.26 


70.0 


11.6 


.17 



As the total quantity of water increased there was a 
relatively small increase in yield. In ordinary practice 
these crops receive small irrigations weekly, or somewhat 
larger irrigations every other week. The most important 
thing in their culture is to keep the soil from becoming 
too dry during the growing period. However, no water 
should be added after the heads are half formed as it may 
cause a splitting of the heads. Cauliflower should be 
treated much the same as cabbage. Lettuce, spinach and 



SUGAR BEETS, POTATOES, ETC. 



309 



300C 




30 



• o 



III 
111 



I 
I 
I I 
I I 




Fig. 84. Yield vs. water (potatoes). 

parsley are crops that feed near the surface and require 
rather small frequent irrigations. The total quantity of 
water required by these crops is small. 

186. Asparagus and celery. — These are important 
and valuable irrigated crops. Asparagus needs water 
chiefly during the cutting season, after which watering 



310 



IRRIGATION PRACTICE 



once a month is ample. Celery is a water-loving crop, 
although if sufficient is added to keep the soil in a moist 
condition, the yield is just as well as if excessive quan- 
tities were added, and the quality is better. 

187. Onions and miscellaneous crops. — Onions should 
be planted in a soil well filled with moisture. A month 
may then elapse before the first irrigation. This crop may 
be irrigated either by the furrow or the flooding method. 
Usually frequent small irrigations are better than infre- 
quent large ones. In middle summer, when growth is 
rapid, it may need much water. When the tops fall, irriga- 
tion should cease. Maturity may be hastened by with- 
holding water when the crop is half grown. The Utah 
Station has tested the effect of varying quantities of 
water on the yield of onions as shown in the following 
table : 

Yields of Onions with Varying Quantities of Irrigation 

Water 



Inches of 
irrigation water 
applied 


Tons per acre 


Yields per acre-inch 
of water 


15 
20 
30 
65 


10.8 
11.0 
16.2 
16.2 


.71 
.55 
.55 

.27 



The law that the yield does not increase in proportion 
to the water applied holds with onions as with other crops. 

Rhubarb requires frequent irrigations during cutting 
time. With good wettings in midsummer, the bud-forma- 
tion for the next year is furthered. 

Tobacco, peanuts and a host of other crops grown in 
the world may be brought under successful cultivation 



SUGAR BEETS, POTATOES, ETC. 



311 



in the irrigated section. These and other crops should be 
grown under irrigation as under humid conditions. Prac- 
tically all of them may be grown successfully from the 
first by remembering a few general principles: The soil 
should contain much moisture at the time of planting. 
The crops should 
always be planted in 
rows. As a general 
rule it is best to irri- 
gate in furrows. Irriga- 
tion should be delayed 
until the plant has 
established its root- 
system well and until 
it really calls for water. 
Irrigation should occur 
every two or three 
weeks. Water should 
be applied liberally at 
the time of flowering. 
Where the rainfall is 
from 12 to 15 inches 
annually, a quantity of 
irrigation water for the season, from 15 to 24 inches, is more 
than enough to make sure of a good yield for any crop. 
More than that is likely to cause deterioration of quality 
and diminution in yield. Less than that often produces 
the best yield. The crops that grow throughout the season 
are watered more than those which have short growing 
seasons. Crops that are leafy require more water than 
those of small leaf surface. Crops planted closely together 
use more water than those planted far apart. All in all, 
more depends ordinarily upon the soil than upon irriga- 




Fig. 85. Irrigated Egyptian cotton. 



312 



IRRIGATION PRACTICE 



tion in making any new crop successful. If the soil is of 
the right kind, and irrigation is practised in moderation, 
more depends upon the careful, persistent cultivation of 
the soil than upon the water or the soil. The irrigation 
farmer needs to remember over and over that irrigation 
is simply the supplementing of the natural rainfall, and 




Fig. 86. Irrigating cantaloupes. 

that any crop grown under natural rainfall may be grown 
with irrigation providing soil and climatic conditions are 
suitable for the crop. 



REFERENCES 

Clark, J. Max. Potato Culture near Greeley, Colorado. United 

States Department of Agriculture, Yearbook for 1904. 
Coit, J. Eliot, and Packard, Walter E. Imperial Valley Settlers' 

Crop Manual. California Experiment Station, Bulletin No. 

210 (1911). 
Corbet, L. C. Suggestions to Potato Growers on Irrigated Lands. 

United States Department of Agriculture, Bureau of Plant 

Industry, Circular No. 90 (1912). 
Grubb, E H. Potato Culture on Irrigated Farms of the West. 

United States Department of Agriculture, Farmers' Bulletin 

No. 386 (1910). 



SUGAR BEETS, POTATOES, ETC. 313 

Grubb, E. H., and Guilford, W. S. The Potato. Doubleday, 

Page & Co. (1912). 
McLaughlin, W. W., and Morgan, E. R. Report on Irrigation 

Investigations during 1905-06. Utah Experiment Station, 

Bulletin No. 99 (1906). 
Nowell, Herbert T. Duty of Water on Field Pease. Wyoming 

Experiment Station, Bulletin No. 72 (1906). 
Roeding, F. W. Irrigation of Sugar Beets. United States Depart- 
ment of Agriculture, Farmers' Bulletin No. 392 (1910). 
Teele, R. P. Review of Ten Years of Irrigation Investigations. 

United States Department of Agriculture, Office of Experiment 

Stations, Annual Report for 1908 (separate). 
Townsend, C. O. Sugar-Beet Growing under Irrigation. United 

States Department of Agriculture, Farmers' Bulletin No. 567 

(1914). 
Welch, J. S. Irrigation Practice. Idaho Experiment Station, 

Bulletin No. 78 (1914). 
Wickson, E. J. Irrigation in Field and Garden. United States 

Department of Agriculture, Farmers' Bulletin No. 138 (1901). 
Widtsoe, J. A., and Merrill, L. A. The Yields of Crops with 

Different Quantities of Irrigation Water. Utah Experiment 

Station, Bulletin No. 117 (1912). 
Widtsoe, J. A., and Merrill, L. A. Methods for Increasing the 

Producing Power of Irrigation Water. Utah Experiment 

Station, Bulletin No. 118 (1912). 



CHAPTER XVI 
FRUIT TREES, OTHER TREES AND SHRUBS 

The pioneers of irrigation planted practically every 
known fruit tree in the early years of their possession 
of the West, and demonstrated that all would grow 
to maturity and bear excellent fruit. Apples, pears, 
peaches, quinces, figs, dates, oranges, lemons, nuts, 
strawberries and all the small fruits, and a host of others, 
have been shown to thrive under irrigation. The people 
of the earth are consuming more and more fruit, and a 
greater demand is being made for fruit of definite color, 
quality and other desirable properties. The control that 
irrigation makes possible, together with the favorable 
climate and soil of the arid region, enables the farmer 
to produce fruit of the quality demanded by the markets. 
Fruit-growing is becoming a great irrigation industry, 
and as time goes on, fruit from the irrigated farms will be 
sent over the whole earth. 

188. Fruit-growing. — Fruit-growing differs in many 
essentials from the production of other farm crops. First, 
there is a high initial expense in preparing the land and 
in purchasing and planting the young trees. Then, only 
after many years of careful supervision, entailing much 
labor, is the first crop obtained. Finally, for many years, 
the trees live and yield harvests, during which the conse- 
quences of the mistakes made in the beginning are made 
evident to the farmer. Therefore, from the first, extreme 
care must be used in fruit-growing. 

(314) 



TREES AND SHRUBS 315 

The methods of planting and maintaining trees are 
not essentially different in irrigated and humid districts. 
Irrigation is the one chief difference, and irrigation is not 
the least important in producing and maintaining orchards 
that justify the great expenditure of -means that must 
be made upon them. In orchards, moreover, the greatest 
irrigation science has been applied, and in them the 
highest duty of water has been obtained. 

Orchards lend themselves well to thorough cultiva- 
tion, which may be one reason for the high duty of water 
in fruit-farming. It is of extreme importance that cultiva- 
tion be practised as thoroughly as possible in orchards. 
The soil must be stirred immediately after each irriga- 
tion, and several times between successive irrigations. 
Both in spring, fall and early growing season should the 
cultivator be at work in the orchard if the farmer expects 
the greatest profit. 

189. Method of orchard irrigation. — Orchards may 
be irrigated by any of the methods already discussed. In 
early irrigation days, the flooding method was most 
generally employed in orchards, and even today this 
method is extensively used in California and some other 
localities. When the flooding method is used today, 
earth ridges are formed half way between the rows of trees, 
making a set of squares with a tree in the middle of each. 
These are filled with water as described in Chapter X. 
The trees themselves are protected from direct contact 
with the water by earth heaped around the trunks. This 
method has the advantage that it covers the whole sur- 
face of soil and insures a uniform penetration of water, 
which has a beneficial effect upon the soil and soil organ- 
isms. However, much work attends the throwing up of 
the ridges and the orchard is made unsightly and difficult 



316 IRRIGATION PRACTICE 

to cultivate by the ridges. In other places the check 
method of flooding is used. The whole orchard is sur- 
rounded by ridges or checks, and water is allowed to flow 
into the basin thus formed. This method is now seldom 
used. The only flooding method of today, besides the 
basin method, is the equivalent of the field ditch method, 
whereby water taken from the head ditch by smaller 
ditches, is led by small ditches, filled to overflowing, over 
the whole orchard. 

The furrow method is the commonly adopted method 
of all orchard irrigation. By this method a permanent 
ditch is built at the head of the orchard. This may be a 
flume or pipe made of wood or concrete. At various inter- 
vals there are openings in the ditch or flume to lead the 
water into the orchard; or if a pipe has been laid under- 
ground, there are standpipes through which the water 
pours out. From this head ditch the water is led by fur- 
rows through the orchard. A head ditch carrying about 
2 second-feet is about right for most orchard work. 

In the furrow irrigation of orchards it is very difficult 
to admit to each furrow the same quantity of water. For 
that reason small lath boxes, already described, are 
employed to connect the head ditch with each furrow. 
Instead of the lath boxes, small permanent pipes are 
often placed at the head of the furrows. The length of 
the furrows on sandy or gravelly soils should usually be 
less than 500 feet, and on clayey, heavy soils, seldom 
more than 600 feet. The shorter the furrow, within prac- 
tical limits, the more probable is the equal distribution 
of water at the head and end of the furrow. The grade of 
furrows preferred in orchard irrigation is a fall of 3 to 4 
inches to each 100 feet. If the land is steeper than this, 
the furrows must be carried around the land in a zigzag 



TREES AND SHRUBS 317 

fashion. This is a very common orchard practice in notable 
orchard districts, as for instance, the Hood River Valley 
of Oregon. 

Under good systems of orcharding, almonds, pears, 
peaches, cherries, apricots and oranges are spaced about 
24 feet apart; apples about 30 feet; walnuts about 38 
feet; and other trees in like proportion. This wide spac- 
ing makes necessary several furrows for irrigation between 
the rows of trees, if the soil is to be saturated thoroughly. 
Young trees have light water requirements, and one fur- 
row, not too far from the row of trees is then usually 
sufficient. Older trees with wide-spreading roots make it 
necessary to move the furrows farther away. As time goes 
on, several furrows are made between the rows of trees, 
so that the farmer is certain that the roots, wherever 
they may be, are given an ample supply of water. How- 
ever, if the furrows are carried too near the trees at the 
beginning of growth, the roots may strike upward and 
remain near the surface. For that reason, the furrow is 
placed at some distance even from the young tree, so 
that the roots will be made to grow downward in search 
of the moisture soaking down from the furrow. By this 
method it is possible to establish deep root-systems, which 
are of first importance in producing trees that may endure 
ooccasional droughts and always make the best use of 
the water stored in the soil by rains or irrigation. 

Small furrows, carrying little water, are usually placed 
about 23^2 feet apart. Deeper ones carrying more water 
are placed 3 to 4 feet apart. Some orchardists place the 
furrows 7 or 8 feet apart but make them very deep, and 
depend on lateral seepage to moisten all the soil. On 
average arid soils it is possible that a distance of 7 or 
8 feet apart for deep furrows is really better than the 



318 



IRRIGATION PRACTICE 



distance of 3 or 
soils it is safe to 
clayey soils; but 
Shallow furrows 
late it has been 
deep furrows are 



4 feet more commonly used. On sandy 
place the furrows farther apart than on 
deep, widely spaced furrows are the best, 
were formerly used extensively, but of 
demonstrated, especially by Fortier, that 
by far the better. 




Fig. 87. Irrigating an apple orchard. 

When furrows are run in one direction between the 
rows of trees it follows that there is a space in the row 
between the trees that is left quite dry. For that reason 
cross furrows are sometimes run between the trees at right 
angles to the main furrows so that the land may be more 
uniformly wetted. To cover the whole orchard uniformly, 
the furrows are often zigzagged across the orchard instead 



TREES AND SHRUBS 319 

of following the rows. While this system does moisten the 
land uniformly, it is complicated and involves consider- 
able expense. Straight furrows running between the rows, 
with occasional cross furrows, is the more satisfactory 
system. 

After each irrigation, the furrow is covered to diminish 
evaporation. The furrows, therefore, are temporary and 
must be made before each irrigation. It is difficult to 
control the water thoroughly even under the furrow 
method of irrigation. Some water, of course, always 
reaches the end of the furrows and is allowed to flow into 
a cross ditch at the end of the furrows which acts as head 
ditch to the furrows below, or this water may be taken on 
to fields of lucern or other crops. (Fig. 87; also Figs. 41- 
56.) 

190. — Time of orchard irrigation. — Fall and winter 
irrigation is very advantageous in the maintenance of 
orchards. In the colder parts of the arid regions, where 
the ground, during winter, is frozen and well covered with 
snow, fall irrigation alone is practised. The wood of the 
trees is allowed to ripen thoroughly before fall irrigation. 
If water is applied too early, so that new growth starts, 
the trees are in danger of winter-killing. In the warmer 
parts of the arid region, with mild, open winters, as in 
Arizona, winter irrigation is of greatest benefit. Lands 
that receive little precipitation in the winter are especially 
benefited by winter irrigation. Districts in which the 
precipitation comes largely in the fall, winter or early 
spring, are not so greatly benefited by fall or winter 
irrigation. In such places the added water may simply 
cause seepage, which is not desirable. 

Unless the soil is dry in the spring, there is no need of 
spring irrigation. As a general rule, trees must not be 



320 IRRIGATION PRACTICE 

irrigated, or very cautiously, when they are in bloom; for 
such early irrigation is said to interfere with the setting 
of the fruit. The proof of this has not yet been made. As 
the hot season advances, water is needed, but the first 
irrigation should be postponed until really needed by the 
orchard. In Washington, where the season begins early and 
there is a high annual rainfall, the first irrigation comes in 
late April or early May, followed by three or four irriga- 
tions, from twenty to thirty days apart. In the drier parts 
of the arid region, where spring comes later, the first irri- 
gation can be postponed until June or even July. In the 
Hood River Valley of Oregon, soils well saturated in the 
spring need no further irrigation until about July 15. In 
Colorado, water is applied to an orchard from two to five 
times a season. In Idaho, where the first irrigation comes 
about June 15, three irrigations in a season are said to be 
sufficient. The Utah practice is the same as that of 
Idaho. As an average, two to four summer irrigations, 
of 3 to 7 acre-inches each, and one fall irrigation should 
be sufficient for deciduous fruits. This means that if irri- 
gation begins in June there will be one irrigation every 
three or four weeks throughout the summer season. 

Orchard soils should not be allowed to dry out too 
much, for an excessive dryness in early or middle summer 
will injure the tree for the whole season. On the other 
hand, over-irrigation tends to decrease fruit-production 
and delay the ripening of the fruit. The farmer, therefore, 
must remember not to check the growth of the fruit tree 
by too little irrigation, nor to irrigate so heavily that the 
formation of buds is decreased and ripening delayed. 
Fruit trees make little growth after July 15, when the 
fruit-buds for the following year are being made. Exces- 
sive irrigations at this time, which force continued 



TREES AND SHRUBS 321 

growth, tend to retard the development of fruit-buds for 
the ensuing year. Fruit-buds seem to develop more 
rapidly when growth is slow, due perhaps to the fact that 
rapid growth consumes the supply of stored food, which 
is necessary in constructing wood or buds. It is the general 
opinion that young peach orchards should not be watered 
after August 1, and that apples or pears should not ordi- 
narily be watered after August 15. Withholding water, 
from these dates, enables the trees to ripen their fruit 
properly, and to produce fruit of high color and fine 
quality. If the soil is well stored with moisture early in 
August, the trees are not likely to suffer if no further 
irrigations are applied. A light green color and dead 
edges of the leaves and the shriveling of the young fruit 
are evidences that the soil moisture supply is so low 
that the root-hairs are drying up. No harm comes to 
a tree that has been irrigated well up to the middle of 
August, even if the soil becomes very dry thereafter, 
although occasionally, under such conditions, the leaves 
become yellow and fall before frost comes. This, how- 
ever, does not injure the tree, and need not worry the 
farmer. 

Citrous trees are really evergreens. They make their 
chief growth in autumn, when the deciduous tree rests. 
Citrous trees are always active. Transpiration goes on 
practically the whole year and such trees must, therefore, 
be provided with water in summer and winter. This 
increases the total water requirements and also the 
number of times that irrigation should be applied. Com- 
mon practice seems to be that, whereas deciduous fruits 
are irrigated three or four times during the season, citrous 
trees must be irrigated at intervals of about a month 
each, leaving the wet season to take care of the trees 
u 



322 IRRIGATION PRACTICE 

without further irrigation. Each irrigation in California 
is in the neighborhood of 3 acre-inches. 

191. Quantity of water for orchards. — There is little 
exact data on the right quantity of water to use in orchard 
irrigation. Orchards need less water than a vigorous field 
of alfalfa. Pears can stand more water than apples; 
apples more than peaches; citrus trees most; the olive 




Fig. 88. On the upper canal. 

endures very little water. The true water requirements 
depend on many factors, such as climate, soil, and age 
and nature of crop. A tree may grow with a very small 
quantity of water which, however, may be insufficient to 
produce fruit. 

The actual duty of water in orchard irrigation varies 
from 60 acres to 400 acres for 1 second-foot of water. 
Fortier states the well-known truth that where most 



TREES AND SHRUBS 323 

water is available, most water is used. For instance, in 
Wyoming, in well-watered sections, the duty of water is 
70 acres per second-foot; in California, where water is 
scarce, the duty is 400 acres per second-foot. Yet, in the 
latter place citrus trees with long growing periods are 
largely grown, and the climate is hotter than in Wyoming. 
The whole question of the quantity of water needed for 
orchards needs careful investigation. It is probably safe 
to say that from 12 to 24 inches is an ample seasonal 
depth of water for orchard crops. More than 6 acre- 
inches is seldom needed in any one month, even under low 
rainfall and high evaporation. That means, for an irri- 
gation season of two months, 12 inches, and of three 
months, the usual limit, 18 inches. The long-season 
citrus fruits seldom need more than 3 acre-inches of water 
per month, although according to Wickson, citrus trees 
require 50 per cent more water for each crop than do 
deciduous trees. Wickson declares, however, that 20 
acre-inches are ordinarily sufficient, annually, for the 
irrigation of citrus trees, and that 10 inches are frequently 
sufficient. 

192. Other conditions of orchard irrigation. — In young 
orchards, and occasionally in old orchards, inter-culture 
is often practised. Corn, potatoes, beets, squash and 
various vegetables or small fruits are planted between the 
rows of trees. Moreover, to maintain the fertility of the 
land, cover-crops are occasionally planted between the 
rows of older trees. Inter-tillage in orchards invariably 
means a higher water requirement than does clean cul- 
ture. The increase corresponds to the degree of inter- 
culture. 

The great danger in orchard irrigation is over-irri- 
gation. Only by moderate irrigation can the root-system 



324 IRRIGATION PRACTICE 

be so developed as to take care of the tree in seasons of 
drought. If too much water be used, the rising ground 
water will kill the roots and thus the trees. Trees that 
have been planted on soils with a water table near the 
surface do not send their roots into the water and are 
not injured; but, when the roots have gone deeply into 
the soil and then are immersed in the rising water, the 
tree is sooner or later killed. Irrigation cannot take the 
place of pruning, cultivation and other approved horti- 
cultural practices. When these are attended to, relatively 
small quantities of water will produce large yields of 
excellent fruit. The orchardist must keep in mind, most 
of all, that if the soil itself is deep it is a splendid water 
reservoir, in which may be stored large quantities of 
water without making connection with the standing 
water. 

There is often a great hurry to make the young tree 
grow as rapidly as possible above ground, when, in fact, 
the main thing is to make the young tree develop a deep, 
vigorous root system. The young tree, during the first 
year or two, does not really use much water; and, if the 
land to be planted to trees is irrigated abundantly before 
planting, and then thoroughly cultivated, there will be 
little need of irrigation during the first year. The second 
is the critical year for the orchard. During this year it 
should be irrigated sparingly, but cultivated well. If too 
much growth is then encouraged, the trees may easily be 
winter-killed, and if the roots are given the wrong habit 
of growth, the orchard may be injured permanently. 
With each year more water is needed, until maturity is 
reached. 

At the town of Hanksville, Utah, the dam supplying 
the irrigation canal broke, and the people, disheartened, 



326 IRRIGATION PRACTICE 

abandoned their homes and their orchards. Five years 
later, every tree that had grown along the ditch banks and 
had, therefore, developed shallow root-systems, was dead. 
Every tree that stood at considerable distance from the 
ditch banks and had, therefore, been compelled to strike 
its roots deeply, was in a most excellent condition and 
carrying small quantities of fruit. These and similar 
experiences demonstrate the very great importance of a 
deep root-system in sections where drought or the driest 
year may come at any time, through climatic variations 
or some accident like the breaking of a dam. 

The quality of irrigated fruit is greatly affected by 
irrigation. Lewis states that irrigation makes larger, 
more elongated, more angular, brighter and more attrac- 
tive fruit. Moderate irrigations reduce the windfalls, and 
produce fruit of high color, fine flavor and good shipping 
quality. Fruit raised by moderate irrigations is pre- 
ferred for drying or canning. Walnuts slip more easily 
from the skin if water has been applied in medium quan- 
tities. Over-irrigation is always an injurious practice in 
fruit-production. 

193. Nursery stock. — Nursery stock must be grown 
in soil kept as far as may be possible at a uniform degree 
of moisture. Nursery stock does not well resist sudden 
shocks of any kind. 

194. Small fruits. — The small fruits, such as dew- 
berries, raspberries, currants, blackberries, strawberries, 
loganberries and gooseberries, are grown readily under 
irrigation, and most of them require very little water. 
Cranberries also have been known to yield well under 
irrigation in especially constructed basins. 

There should be an abundance of water at planting, 
and some water should be kept in the soil throughout the 



TREES AND SHRUBS 327 

growing season. Little water should be applied at flower- 
ing time and much water at fruiting time. The wood 
should be allowed to ripen for the fall in comparatively 
dry soil. Ordinarily, irrigation should be stopped about 
August 1. Then, in late October or early November, 
another irrigation may be given, to help produce a better 
crop the following year. The small fruits should all be 
irrigated in furrows, and the water should not be allowed 
to touch the plant. In general, the principles that have 
been developed with regard to other crops hold with 
these. 

195. Grape-vines. — The grape cannot stand much 
water. In fact, grape-vines grow without irrigation over 
a large part of the arid regions where the annual rainfall 
is 10 to 15 inches. The excessive use of water is the chief 
cause of the troubles of the vine-growers. Excessive irri- 
gation causes mildew and similar troubles, and injures the 
shipping qualities of the grapes. In California, water is 
withheld from grape-vines even to the point where the 
leaves begin to fall. Very superior fruit of high sugar 
content and excellent flavor results. Irrigation is done by 
furrows. The furrows should be run midway between 
the rows; for, if they are too near, mildew may set in, 
and the vines will trail in the mud. In vineyard culture, 
the rule is to water well when watering and to cultivate 
several times before the next irrigation. Coit, speaking of 
conditions in the Imperial Valley, suggests that the last 
irrigation should be given at the commencement of the 
ripening period, and that irrigation during the last stages 
of ripening is dangerous. The grape-vine must be so 
grown as to have deep roots, which can be done only by 
the consistent use of moderate quantities of irrigation 
water. 



328 



IRRIGATION PRACTICE 



196. Plants for ornament and comfort. — Shade trees, 
shrubs, flowers — as windbreaks, along the streets or in 
the gardens — are all grown easily under irrigation. They 
require, generally, the same treatment as other crops. 
Such crops should be watered regularly. During the 




t> S ^K,- d& 



ESMW^fR"*' i iS?*im3f- g 



Fig. 90. An irrigated date palm orchard in Arizona. 

season, more water can be given them than crops grown 
for commercial purposes. Forest trees are seldom grown 
except for ornamental purposes. In a few sections of the 
country, where the settlements are far from the railroad 
and coal mines, trees, notably the poplars, are grown to 
furnish fuel for the farmers. Trees for this purpose are 
grown along the ditch banks, and receive only such water 
as they absorb directly from the water seeping through 



TREES AND SHRUBS 329 

the ditch bank. When such trees are grown in plantations, 
the quantity of water applied and the manner of appli- 
cation are practically as for orchards, except that more 
water may be applied, since the main purpose is to produce 
the largest possible wood growth. 

Practically every tree, shrub and flower known to man, 
which can endure the soil and climatic conditions of the 
irrigated area, may be grown under irrigation. Irri- 
gation is nothing more than supplementary rainfall. 
Wherever rainfall is desirable for plants, irrigation is 
desirable also. 

REFERENCES 

Coit, J. Eliot. Olive Culture and Oil Manufacture. Arizona Experi- 
ment Station, Bulletin No. 62 (1909). 

Coit, J. Eliot, and Packard, W. E. Imperial Valley Settled 
Crop Manual. California Experiment Station, Bulletin No. 
210 (1911). 

Etcheverry, B. A. Practical Information on Irrigation for British 
Columbia Fruit Growers. British Columbia Department of 
Agriculture, Bulletin No. 44 (1912). 

Fortier, Samuel. Irrigation of Orchards. United States Depart- 
ment of Agriculture, Farmers' Bulletin No. 404 (1910). 

Fortier, Samuel. Guide to Irrigation Practice on the Pacific 
Coast. National Irrigation Congress, Bulletin No. 4 (1907). 

Herrick, R. S., and Bennett, E. R. The Colorado Raspberry 
Industry. Colorado Experiment Station, Bulletin No. 171 
(1910). 

Lewis, C. J., Kraus, E. J., and Rees, R. W. Orchard Irrigation 
Studies in the Rogue River Valley. Oregon Experiment Sta- 
tion, Bulletin No. 13 (1912). 

Long year, B. O. Strawberry Growing in Colorado. Colorado 
Experiment Station, Bulletin No. 140 (1909). 

McClatchie, A. J. Winter Irrigation of Deciduous Orchards. 
Arizona Experiment Station, Bulletin No. 37 (1901). 

Paddock, Wendell, and Whipple. O. B. Fruit Growing in Arid 
Regions. Chapter XIII. The Macmillan Company (1910). 



330 IRRIGATION PRACTICE 

Smith, Ralph E. Walnut Culture in California. California Experi- 
ment Station, Bulletin No. 231 (1912). 

Whipple, O. B. Grape Growing. Colorado Experiment Station, 
BuUetin No. 141 (1909). 

Wickson, E. J. Irrigation in Fruit Growing. United States Depart- 
ment of Agriculture, Farmers' Bulletin No. 116 (1900). 

Wickson, E. J. Irrigation among Fruit Growers of the Pacific 
Coast. United States Department of Agriculture, Office of 
Experiment Stations, Bulletin No. 108 (1902). 



CHAPTER XVII 

THE DUTY, MEASUREMENT AND DIVISION 

OF WATER 

In the foregoing chapters have been elucidated the 
known laws governing the relationship that exists between 
soils, plants and water. Results obtained under well- 
controlled laboratory or experimental field conditions may 
often differ from those obtained in general field practice. 
This chapter, therefore, discusses the practical duty of 
water and the methods of measuring and distributing 
irrigation water, so that ideal conditions may be ap- 
proached. 

197. The duty of water. — The duty of water, a term 
long since coined, means the quantity of water needed to 
mature crops. It may be expressed in various ways. 
Sometimes the duty of water is expressed as the number of 
pounds of water required to produce one pound of the 
dry matter of the crop; under other conditions, as the 
depth of water over the field, required during the growing 
season, to produce the crop. More commonly, however, 
the duty of water is expressed as the number of acres 
that may be irrigated by a definite quantity of water, 
say a second-foot, flowing continuously throughout the 
growing season. In Canada, the United States, India, 
Australia and other irrigated countries, this is by far 
the most common method of expressing the duty of 
water. The reason for this popularity seems to be that 
irrigation canals are generally taken directly from 

(331) 



332 IRRIGATION PRACTICE 

streams having a continuous flow during the irrigation 
season. 

Various units for measuring water are used in different 
parts of the country, such as the miner's inch, but the 
only one in modern general use is the cusec or second-foot, 
which means 1 cubic foot of water passing a given point 




Fig. 91. Canal crossing river in an inverted syphon. 

each second of time. The duty of a given stream would 
then be the number of acres irrigated per second-foot, 
flowing continuously during the season. This duty may 
easily be converted into acre-inches or acre-feet of water. 
One second-foot, flowing for twenty-four hours, will 
cover 1 acre to a depth of nearly 2 feet. If the time is 
known during which a second-foot of water has been 
flowing over a given area, it is but a moment's calcula- 



DUTY AND DIVISION OF WATER 



333 



tion to determine the depth to which the land has been 
covered. 

The time during which a given volume of water flows 
is of first importance in determining the duty of the 
stream. A canal carrying 10 second-feet of water may be 
filled from May 1 to November 1; and during that time 
may irrigate 1,000 acres of land. The quantity of water 




Fig. 92. Looking down the Bear River Canal. 

passing through the canal during the six months in 
question would cover the 1,000 acres to a depth of nearly 
39 inches. In fact, however, the water was used for irri- 
gation purposes only about seventy-five days out of the 
six months and the actual depth of water given the crop 
was only about 18 inches. The duty of water expressed 
as the area covered by a given volume of water, flowing 
continuously, may, therefore, become very misleading 



334 IRRIGATION PRACTICE 

unless it is carefully specified that the water was used 
during a certain number of days. 

Canals taken directly out of the river usually carry 
water from early spring until late fall, but the water so 
delivered before and after the irrigation season should 
not be charged to the duty of water. When the waters 
are held back in reservoirs, water is of course allowed to 
flow through the canal only during the irrigation season. 

The relationships existing among the quantity of flow- 
ing water, the number of acres to be irrigated and the 
depth to which the land will be covered may be shown in 
simple formulas: 

A = Area to be irrigated. 

D = Duty of water, that is the acres matured by 1 

second-foot flowing continuously for a definite 

period. 
B = The time in days 1 second-foot flows to mature 

crop. 
S = The depth in inches of the given volume of water 

over the area irrigated. 
F = The discharge of second-feet necessary to irrigate 

the given area A, with the duty D. 
The following relationship may then be established: 

S = — X 23.8. 

„ A AS 



D BX23.8 

198. Classes of duty. — The theoretical duty of water 
is never quite realized in practice. The term "duty of 
water" does not refer to the theoretical deductions in 
laboratory experiments, but refers invariably to the water- 
cost of crops under practical conditions. It is, therefore, 



DUTY* AND DIVISION OF WATER 



335 



a term which cannot, under present conditions, be fixed. 
As time goes on, and irrigation practices are improved, 
there will be an increasingly high duty of water obtained 
in the irrigated section. 

The absolute duty of water means the sum of the water 
applied to the plant in irrigation and the water supplied 
from the soil moisture and by rains during the growing 
season. This duty is usually expressed as the depth in 




Fig. 93. Lateral outtake from large canal. 

inches over the land. For instance, in a certain experi- 
ment, 6.4 inches of water were taken from the soil; 15.3 
inches were added by irrigation, making a total of 21.7 
inches, the absolute duty. 

The net duty of water means the area of land covered 
by the water received by the farmer at the farm head- 
gate. It is practically identical with the absolute duty, 
except that the water stored in the soil and the rains during 
the summer are not taken into account. 

The gross duty of water means the area of land served 
by the water at the intake of the canal, or occasionally 



336 IRRIGATION PRACTICE 

at the intake of the large lateral. It is the duty for the 
whole system and is of primary interest to the engineers 
who design irrigation systems. In transit from the head 
of the main canal to the farm where the water is applied 
to the crops, large volumes of water are lost by evaporation 
and seepage, and the duty of water for the system does 
not at all represent the actual water requirement of the 
crops grown under the system. The net duty is therefore 
of prime value to the farmer whose chief interest is in the 
water actually received by him at his farm. 

199. Determination of duty of water difficult. — The 
duty of water under any irrigation system is always diffi- 
cult to determine. The soil, climate, methods and time 
of application and many other factors do much to increase 
or decrease the area that may be served by a given quan- 
tity of water. The reservoirs and canals themselves, 
whether lined or unlined, whether passing over gravelly 
strata or clay beds, determine in large degree the gross 
duty under the system. After all such factors have been 
taken into consideration, there remains, as a disturbing 
factor, the law that the more water is added to a crop, the 
smaller the yield to the unit of water. This law of increas- 
ing water-cost brings always to the front the question of 
whether much water shall be used to obtain the largest 
possible yield an acre, or whether moderate quantities 
shall be used to obtain the largest yield from each acre- 
foot of water. There is a depth of water for each set of 
land, crop and water conditions, which produces the 
greatest profits. When water is added above or below this 
point the profitableness decreases. This point of optimum 
duty will, as our knowledge increases, be determined for 
different crops and irrigation projects. 

An example will illustrate what is meant by this point 



DUTY AND DIVISION OF WATER 



337 



of highest profitableness or optimum duty. A beet field 
is supplying beets to the factory at a contract price of 
$5 a ton. The total cost of producing the beets, includ- 
ing interest on the investment, may be assumed to be $60 
an acre. The following table may then be constructed on 
the basis of the crop yields in the Utah experiments on 
the effect of varying quantities of water on the growth of 
crops: 



30 acre- 
inches 
spread 
over 



1 acre 

2 acres 

3 acres 

4 acres 



o a 


.2 In 

a> O 
2 t - 


tj a 


h 

O <n 

■a-° 

■S o 


o 
0.3 

O 4) 
■1 

22 


g 
o 

83 

u 
a 

a 

o 


m 
O 
« 

o 


<S ° 


*& 


H" 


ft-" 


O 


Q 




30.0 


21.0 


21 


$5 


$105 


$60 


$60 


15.0 


19.5 


39 


5 


195 


60 


120 


10.0 


18.6 


56 


5 


280 


60 


180 


7.5 


16.3 


65 


5 


325 


60 


240 



O O) 

•-a 

-g o 
55 ^ 



$45 
75 

100 
85 



Under the above conditions, the largest net income, 
$100, was obtained when 30 acre-inches were spread over 
3 acres. When spread over less or more land than this 
the net income decreased. Similar results must be deter- 
mined for all of the standard crops, so that for any set of 
conditions the most profitable depth of water may be 
known. 

In different sections of the irrigated regions, 1 second- 
foot of water serves from 25 to over 300 acres, with an 
average near 75 to 100 acres. This great variation is 
partly due to the differences in rainfall. Wherever the 
rainfall is high, less irrigation water is required to mature 
crops. This is not the main cause of the varying duty of 
water, for the highest duty is usually found where the 
rainfall is light, as in southern California. Differences 
v 



338 IRRIGATION PRACTICE 

in the duty of water lie rather in the practices of the farmer, 
who usually feels that the more he irrigates his crops, the 
greater will be his reward. Every irrigation farmer is 
something of a water hog. His safety lies in the irrigation 
canal, especially in the lateral which leads to his farm. 
One of his main efforts is to secure the largest possible 
quantity of water for his land. As a consequence, the 
varying duty of water can ordinarily be correlated with 
the quantity of water available in various localities. 
Wherever water is abundant, the duty is low; wherever 
limited, the duty is high. At the upper end of the canal 
the duty is less than at the lower end, for the farmer at 
the head has the first chance and uses all he can get, 
usually to the detriment of his crop. 

200. Duty of water in Africa. — Egyptian irrigation 
antedates written history. The early Egyptians gave 
careful attention to the development of a permanent 
system of irrigation. The modern government of Egypt 
has likewise given very careful attention to irrigation and 
some of the largest modern irrigation projects have been 
constructed in Egypt. 

The climate of Egypt is very arid. According to Sir 
William Willcox, the average annual rainfall at Alexandria 
is about 9 inches, at Cairo about 1J4 inches, and at 
Assuan practically no rain falls. Under such a dry climate, 
the water requirements of crops should be very high, 
and the duty of water very low. As reported by Willcox, 
during an irrigation season of about seventy-five days, 1 
second-foot has a duty for cotton and other dry crops of 
115 acres; for rice, 60 acres. This is not far from the aver- 
age results obtained in other countries where much more 
rain falls. Nevertheless, the methods of irrigation prac- 
tised in Egypt tend to waste considerable portions of 



DUTY AND DIVISION OF WATER 339 

water, and make it unlikely that the duty as above given 
represents the most economical use of water. When the 
Nile overflows, water is conducted into large basins and 
allowed to stand there until the silt carried by the river 
water is deposited and the soil itself has become thor- 
oughly saturated with water. Afterwards the surface 
water is allowed to flow back into the Nile. This makes it 
certain that plants do not use all the water actually applied 
to the soil. Moreover, the above results represent the 
gross duty of water in Egypt. Few studies have been 
made of the net duty, but since the gross duty varies 
little from that obtained in other sections of the world, 
it is likely that the net duty is not greatly different from 
that obtained in other parts of the world. 

Some investigations have been made also on the duty 
of water in southern Africa. According to Mawson, the 
duty of water in South Africa, under an annual rainfall 
of 20 to 35 inches, is, for grain, 115 acres; for vegetables, 
100 to 180 acres; for cereal crops, 140 to 200 acres; for 
sugar-cane, 50 to 70 acres; for fruit trees, 200 to 300 acres. 
In the Cape Colony, the duty of water has been found to 
vary from 150 to 285 acres, although two crops were raised 
on the land. In the Transvaal, not quite 24 acre-inches of 
water are applied to land for the production of crops. 

201. Duty of water in Asia. — In Asia, as in Egypt, 
irrigation has been practised from before written history. 
The best example of Asiatic irrigation is India. More 
systematic irrigation work has probably been done re- 
cently in India than in any other part of the world, 
unless it be the recent irrigation progress in western 
United States and western Canada. 

The rainfall of India varies greatly, from the highest 
in the world to a condition of extreme aridity. Over the 



340 



IRRIGATION PRACTICE 



Ganges delta, the average annual rainfall varies from 60 
to 70 inches, whereas over the Northwest Provinces it is 
in the neighborhood of 25 inches. 

The duty of water in India has been investigated under 
government supervision, and much has been published 




Fig. 94. Headgate of a canal. 

concerning it. R. B. Buckley, the chief authority on 
East Indian irrigation, states that the gross duty of water 
during the wet season — from June to October — varies 
from about 80 to 170 acres to the second-foot. During 
the cold season — from November to March — the duty of 
water varies from about 90 to 200 acres to the second-foot 
of water. The duty of water varies greatly, even under 
the same canal, if different sections are considered. In 
India, as elsewhere, it seems to be true that the more 



DUTY AND DIVISION OF WATER 341 

water available, the more used. Moreover, varying seepage 
in different localities causes a varying gross duty of water. 
In one exhaustive study of the duty of water, it was found 
that under a given system, 20 acre-inches were actually 
used for the production of crops; while in another place 
four irrigations of 2J^ acre-inches each, or a total of 
10 acre-inches, produced abundant crops of wheat. 
Kennedy, who carried on experiments under the Barri- 
Doab Canal, found that wheat, barley, coffee, Indian 
corn and cotton required during the season 10.6 inches 
of water; and sugar-cane 25.7 inches. These results show 
that the water requirements of crops in India are practi- 
cally identical with those in America and other countries 
of the world. 

The loss of water from the main Indian canals varies 
from 20 to 75 per cent and, consequently, the net duty of 
water in India is much greater than the gross duty. In 
one series of investigations it was found that even the lat- 
erals from the main canal served a much larger area than 
the whole canal, per second-foot of water, the difference 
rising occasionally to 30 or 40 per cent. 

Under several of the Indian canals, 160 acres have 
been adopted as the duty of water for 1 second-foot under 
the whole system. This compares very favorably with 
present practices in the United States. 

202. Duty of water in Europe. — Irrigation is generally 
practised in Europe, especially in France, Spain and Italy. 
In these latter countries, irrigation goes back many 
hundreds of years, and the methods now followed are 
based upon the experience of centuries. True, in southern 
Europe, irrigation is not a matter of life and death, as 
in the more arid sections of the world, but it has done and 
is doing much to increase the wealth and prosperity of 



342 IRRIGATION PRACTICE 

southern Europe, for, without irrigation, some of the most 
fertile sections of southern Europe would be of mediocre 
producing power. 

The duty of water under European canals does not 
differ greatly from that observed under canals of other 
countries. In France, the duty has been found to vary from 
about 40 to nearly 200 acres to the second-foot of water. 
The lower duty of water prevails where water meadows 
are maintained, which are not a true form of irrigation 
agriculture. Under the carefully managed canals of 
France the duty ranges from 100 to nearly 200 acres to the 
second-foot of water. In Italy, the duty of water varies 
from about 40 to 100 or more acres per second-foot, and 
occasionally reaches 300 acres where Indian corn and 
similar crops are raised. In Spain, where economy in the 
use of water has been carried to a high degree, an average 
duty, under twenty canals, was found to be 172 acres to 
the second-foot of water. As an average of one series of 
measurements under the chief canals of France, Italy and 
Spain, 1 second-foot of water serves 239 acres of the stand- 
ard crops of those countries. Generally speaking, there- 
fore, the duty of water in southern Europe is somewhat 
higher than in Egypt, India or the United States. 

203. Duty of water in South America. — Few data 
exist concerning the duty of irrigation water in South 
America. In prehistoric times, large irrigation projects 
existed in South America, the remains of which give 
testimony of the excellence of South American irrigation 
in earlier days. In northern Peru, which is practically 
rainless, it is reported that the duty of water is 160 acres 
to the second-foot of water; and in northern Chili, which 
is also practically rainless, the duty is about 190 acres to 
the second-foot of water. These figures are averages, for 



DUTY AND DIVISION OF WATER 343 

special districts. It is not likely that any unusually high 
duty of water prevails in South America. 

204. Duty of water in Australia. — Irrigation on a large 
scale is just beginning to be developed in Australia. The 
methods there adopted are based upon the best practices 
of the world, notably upon those of the United States. 
The duty of water, as it is developed in Australia, does 
not differ materially from that of North America. Many 
of the projects are comparatively new and the duty is 
low, but will become higher as more complete irrigation 
practices are adopted. 

205. Duty of water in North America. — The chief 
irrigated section of North America covers western Canada 
and the western United States. These two districts are 
so similar in climatic and soil conditions that whatever 
is true of one is generally true of the other. Some excellent 
duty of water experiments have been made for this section, 
by the United States Department of Agriculture under 
the direction first of Elwood Mead and later of Samuel 
Fortier. The gross duty of water was determined for 
a number of representative canals in all of the western 
states. As a general result, Teele declares that "It appears 
that 33^2 to 4 acre-feet are required at the heads of unlined 
earth canals. This can be taken safely as a basis for 
computation." This means that the duty of water for 
1 second-foot, flowing for 60 days, varies from 34 to 
27 acres; flowing for 120 days, from 68 to 54 acres, 
and flowing for 180 days, from 102 to 80 acres. This gross 
duty for western North America does not represent, even 
approximately, the net duty of water, for the irrigation 
investigations of the United States Department of Agri- 
culture have shown for a series of representative canals 
that nearly 60 per cent of the water is lost between the 



344 IRRIGATION PRACTICE 

headgate of the canal and the laterals, and undoubtedly 
much of the remaining 40 per cent is lost between the 
heads of the laterals and the farms. Observations were 
also made by the government investigators on the quan- 
tities of water actually applied to crops, with average 
results as follows: Alfalfa, 32 inches; wheat, 18 inches; 
barley, 16 inches; potatoes, 28 inches; sugar beets, 25 
inches, with an average for these crops of about 23 acre- 
inches. For an irrigation season of about ninety days, 
this would mean a net duty of 100 acres. This is much 
larger than the gross duty as above given. The losses 
from the canals are always large, averaging 5.77 per cent 
per mile; and Fortier declares that perhaps less than one- 
third of the water diverted by the canals is actually used 
by the crops. 

206. Bear River Canal experience. — One of the most 
notable canals in western America is the Bear River 
Canal, which began its actual operations in 1891. Its 
first duty of water was 40 acres for six months for each 
second-foot of water, or a depth of 4.2 feet during the 
six months. In 1903, after twelve years of experience, it 
was obvious that too much water was being used. The 
ground water table was rising rapidly near the surface, 
alkali was becoming visible in certain low sections, and, 
all in all, the evils from over-irrigation were observed. 
Careful measurements were then made of the water 
delivered, and attempts were made to increase the duty 
of water. For four years thereafter, 6,000 measurements 
were made at the head of the canal, at the heads of the 
laterals, and at the gates to the individual farms. Accord- 
ing to Wheelon, it was found in 1903 that a duty of 67 
acres per second-foot prevailed. In 1904, this had been 
raised to 120 acres, and in 1905 to 138 acres. These 



DUTY AND DIVISION OF WATER 345 

duties were calculated from the measurements taken at 
the heads of the laterals and are smaller than would be 
the case were measurements made at the farms them- 
selves. During these years of increasing duty, crop- 
yields were equally good, and crop quality was improved. 
The increasing duty of water under this system is still 
going on, with the result that farming conditions are 
being greatly improved. This is the history of all the 
larger canals in America that have received competent 
and constant supervision. The duty of water is steadily 
increasing throughout the whole of western America. 

207. Idaho results. — A series of recent investigations 
in Idaho further brings out the present duty of water in 
western America. Bark measured the quantities of water 
used by 168 Idaho farmers. Most of these farmers had 
been farming only a few years, and since the duty of 
water is always lowest at the beginning of irrigation prac- 
tice, the measurements represent maximum use. The 
irrigation season for grain varied from thirty-six to forty- 
six days, and for alfalfa from ninety-six to one hundred 
and twenty-two days. It was found that the crops re- 
ceived on an average practically 2 feet, or 24 inches of 
water, which, for an irrigation season of four months, would 
be equivalent to about 120 acres to the second-foot of water. 
Where water was plentiful, much was used; where water 
was scarce, little was used. Moreover, it was found that 
the entire need for water fell on the four months, May to 
August inclusive. It is likely that for all ordinary crops 
the irrigation season seldom exceeds four months and in 
many cases is covered by two months. 

208. Miscellaneous results. — H. M. Wilson, a high 
authority on irrigation matters, presents the following as 
the duty of water for 1 second-foot of water: In western 



346 IRRIGATION PRACTICE 

United States it varies from 60 to 300 acres; where water 
is most abundant it varies from 60 to 120 acres; where 
water is less plentiful it varies from 100 to 150 acres, 
occasionally rising to 200 acres; where water is very scarce, 
as in southern California, it rises to 300 acres. There are 
records to show that the duty of water has reached even 
1,000 acres to the second-foot of water, but such figures 
are as yet exceptional and need not be given serious con- 
sideration as part of present-day practical irrigation 
agriculture. 

Elwood Mead, one of the world's chief irrigation 
authorities, declares that the duty of water in the United 
States is on the average quite as high as in the older 
countries, but predicts that the duty will be doubled as 
more perfected methods of agriculture are adopted. 

F. H. Newell, the illustrious director of the Recla- 
mation Service of the United States, believes that for good 
farming an average of 12 acre-inches for each acre, during 
the irrigation season, should be enough, except for alfalfa 
and certain similar crops. This, for a four month's irri- 
gation, is a duty of 206 acres. Newell further states that 
the duty of water often reaches 250 to 500 acres to the 
second-foot of water. 

209. The Utah results. — The careful studies of the 
Utah Station on the water requirements of crops indicate 
that, when the natural precipitation is properly conserved, 
even 6 acre-inches an acre will produce fairly good yields 
of all the ordinary crops. If more water be applied the 
yield is smaller in proportion. The Utah results would 
lead to the belief that where the annual rainfall is from 
12 to 15 inches a depth of water from 10 to 20 inches is 
best for ordinary farm crops, and that the best quantity 
lies nearer the smaller figure. A depth of 12 inches prob- 



DUTY AND DIVISION OF WATER 347 

ably represents the average requirement of ordinary farm 
crops, providing the water is measured at the intake to the 
farm. Should this be increased to 20 inches it would still 
be much less than the quantity ordinarily applied. A 
depth of 12 acre-inches equals a duty of 120 acres per 
second-foot for sixty days, or 180 acres for ninety days, 
or 240 acres for one hundred and twenty days. These 
figures probably approximate the normal duty for western 
America, under present conditions. 

The new duty of water must be based upon all the 
knowledge in the possession of man. The water in the 
streams must be used to cover the largest possible area 
so that more men may be given employment and more 
families maintained upon the irrigated lands. 

THE MEASUREMENT OF WATER 

210. Need of measuring water. — Farmers keep ac- 
counts of the area of land under cultivation, the yields of 
crops per acre and the money received for each bushel of 
grain or ton of alfalfa, but often fail to keep track of the 
quantity of water used in irrigation. The whole discussion 
of the preceding chapters is, however, based on the thesis 
that irrigation water may be and should be measured. 
Especially is this necessary where water is more valuable 
than the land, and where it is, therefore, more important 
for the farmer to obtain a large yield to the acre-foot of 
water than to the acre of land. Moreover, if water, from 
the beginning of irrigation, had been measured, less land 
would have become water-logged or subjected to the rise 
of alkali. Finally, there will always be disputes about 
water-rights, and after water-rights are established the 
rulings of the courts must be literally obeyed, so that 



348 



IRRIGATION PRACTICE 



peace may prevail in irrigation communities. What the 
surveyor does in promoting peace as he establishes 
boundary lines for fences between farms, the modern 
irrigation engineer does as he determines the quantities 
of water each farmer and his neighbor are receiving from 
the canal or river. 

In the beginning of irrigation in this country, when 
the pioneers were few and had an abundance of water, it 
is evident that there was not so much need for the meas- 
urement of water as at the present time. As more settlers 




arrived, all the waters were taken up, and there came a 
crying need for suitable devices for measuring and dividing 
water. A perfected system of irrigation agriculture cannot 
come until measurements are made of the flowing water 
in the natural river channels, in the main canals, in the 
laterals and at the headgate of each farm. In fact, the 
measurement of water is the great irrigation need of the 
day, in the face of which all other needs vanish. All that 



DUTY AND DIVISION OF WATER 349 

has been done in the gathering of information concerning 
the relations of soils and crops to water is practically 
useless unless the knowledge be applied under conditions 
of carefully measured water. 

211. Who shall measure the water? — The company 
controlling the irrigation system should conduct measure- 
ments and deliver to each farmer at his own headgate 
and at certain periods a definite number of cubic feet of 
water. The complexity of irrigation agriculture, however, 
makes it evident that a new kind of irrigation engineer 
must arrive who must stand between the canal corpora- 
tion and the farmers drawing water from the canal. He 
must know enough engineering to measure, divide and 
distribute water and to keep up the system of canals and 
laterals, and enough of agriculture to define the quantity 
of water for different soils and crops. A big step onward 
will be taken when canal owners and farmers insist upon 
such a trained water-master. However, in this matter of 
water-measurement the farmer must be independent. He 
should understand the simple ways of measuring water 
accurately. Even when the canal management delivers 
definite quantities of water, it becomes the business of 
the farmer to distribute this water correctly on the fields 
of the farm, and this can be done only by employing sat- 
isfactory measuring devices. 

212. Classes of measurement. — Only under the few 
canals of moderate capacity and early water-right, or 
from ample reservoirs, can the farmer depend on receiving 
the same quantity of water from year to year. In most 
districts the total quantity of water taken in by an irri- 
gation system depends upon the quantity of water flowing 
in the river which, in turn, depends upon the varying 
seasons. Except for certain primary water-rights, or 



350 



IRRIGATION PRACTICE 



small canals or canals drawn from reservoirs, they who 
take water out of a river have right only to a definite 
proportion of the total flow. In a dry as in a wet year 
this proportion remains the same. For instance, if there 




Fig. 96. Lyman rectangular weir. 

are 500 shares in such a canal company, each share will 
receive to o of the total flow in the canal whether the 
flow be large or small. 

There are, therefore, two classes of measuring devices : 
(1) Divisors, for the purpose of dividing streams into 
halves, quarters or other fractions, independently of the 
volume; (2) modules, for the purpose of measuring the 
absolute volumes of water that flow through canals or 
ditches. The divisors can be made satisfactorily only 
after proper and satisfactory modules have been estab- 
lished. 

A great variety of water-measuring devices exists. 
In the beginning of modern irrigation there were no 



DUTY AND DIVISION OF WATER 



351 



special methods for measuring water. Ordinary gates, 
placed at the heads of the laterals, were raised or 
lowered by the water-master to send volumes of water, 
equal to the eye, down the laterals to farmers owning 
practically the same water-rights. Later, with the increas- 
ing value of water, better measuring devices have been 
adopted. 

The simplest devices for measuring the quantity of 
water flowing in a channel are those known as weirs or 
overfalls. A board is placed as a check across the stream. 
Into the board is cut a notch through which the water 
flows. The weir method of measuring water has been 
investigated long and carefully, with the result that in 
some form it may now be used safely and easily by the 
farmer. The chief objection to the use of weirs in irriga- 
tion is the tendency of the weir to become filled with silt if 
the water carries sediment. When this occurs, the meas- 
urements are less reliable and the weirs must, therefore, 
be cleaned frequently. 




Fig. 97. Longitudinal section of Lyman'3 weir 



Three kinds of weirs are used successfully for water 
measurement. First, the rectangular weir, which is best 
known and most certain, for it has received most study 
by engineers. It is not, however, the simplest, because 
the water flowing over the weir contracts at the bottom 
and sides, and this contraction varies as the depth of the 



352 IRRIGATION PRACTICE 

water or the length of the weir increases. The necessary 
corrections for this variation complicates the use of the 
rectangular weir. Many irrigation engineers, however, 
well acquainted with irrigation, insist that for practical 
purposes no weir has taken the place of the rectangular 
weir. Second, the trapezoidal weir, which has largely 
replaced the rectangular weir in irrigation. The trape- 
zoidal is like the rectangular weir, except that the sides of 
the notch slope away slightly, making a trapezoidal, 
instead of a rectangular, opening through which the water 
flows. The sloping sides are intended to correct auto- 
matically the loss of water due to the contraction. Over a 
trapezoidal weir 2 feet long, all else being equal, twice as 
much water is supposed to flow as over one 1 foot long. 
This is not true of the rectangular weir. The first trape- 
zoidal weir with this purpose in view was devised by the 
Italian engineer Cippoletti, and the weir has been named 
the Cippoletti weir by L. G. Carpenter, of Colorado, 
who was first to call the attention of the American public 
to this form of weir. In America, Canada, Australia and 
other countries it is practically the only weir used by the 
irrigator. Third, the triangular weir, the notch of which is 
in the form of a triangle. Its chief advantage is that only 
the depth of water flowing over the triangle needs to be 
measured. Very satisfactory results are obtained by the 
use of the triangular weir, and it is likely to increase in 
favor. With our present knowledge, triangular weirs 
seem suitable chiefly for small streams. 

Recently, Lyman has given careful and exhaustive 
study to this subject, with the result that he has devised 
methods whereby water may be correctly and easily 
measured in flowing streams, without the use of weirs. 
(Figs. 96, 97.) 



DUTY AND DIVISION OF WATER 



353 



213. The Cippoletti weir. — The sides of the notch of 
the Cippoletti weir slope outward at the rate of 1 inch 
horizontally, to 4 inches vertically. The notch of the weir 
is always made with a beveled edge of 30° or more down 
stream so that the water always flows over a sharp edge. 
To maintain the sharp edge, the weir should be faced on 
the inside, or up stream, with iron strips, placed even 
with the beveled edge. The distance from the bottom of the 
weir box to the top of the 
crest should be at least 
two times the depth of 
the water flowing over 
the crest. The weir 
should be installed where 
the approach of the water |£jjj 
is straight, long and level. 
As the water passes over jffij 
the crest, it should flow 
very slowly, not more 
than 6 inches a second for a weir 6 feet wide. The weir 
must be placed at right angles to the stream, with the crest 
absolutely horizontal. Provision should also be made for 
washing out the accumulating sediment by making the 
weir movable, so that it may be raised from time to time. 
In many rivers or large canals the weirs are movable and 
are kept above the stream except when measurements are 
taken. Below the weir, where the water falls over the 
crest, there should be sufficient depth, so that the water 
below the weir does not interfere with the flow over the 
crest. There should always be a free circulation of air 
under the jet of water falling over the weir. When a weir 
of known crest length has once been installed, it is neces- 
sary to determine only the depth of water above the 
w 




Fig. 98. Cippoletti weir. 



354 



IRRIGATION PRACTICE 



crest, some distance back from the weir itself, where the 
overfall has not yet begun to curve the water downward. 
Then, by the use of tables (See Appendix B), the quantity 
of water in cubic feet a second passing over the weir 



sao 




Fig. 99. Details of Cippoletti weir. 

may be determined. Moreover, by use of these tables 
the size of the weir necessary for a given flow of water 
may be found. (Figs. 98, 99.) 

However, even the use of tables is somewhat unsatis- 
factory and inconvenient for the farmer actually at work 
in the field. For that reason, plates have been devised, 
that may be screwed to the side of the weir box, which 
show by inspection the number of cubic feet of water 
passing over the weir every second of time. (See Fig. 100.) 



DUTY AND DIVISION OF WATER 



355 



Naturally, a different plate must be made for each length 
of weir. Once such plates are installed, however, the 
labor of reading weirs is reduced to a minimum. The whole 
question of weir measurements is now being critically 
examined at the Colorado Experiment Station, in cooper- 
ation with the United States Department of Agriculture. 
The weir in some form will undoubtedly be the standard 
measuring device of the irrigation world. 

214. Divisors. — With the Cippoletti weir, the division 
of water may be performed easily and accurately. Since 
the slanting sides of the Cippoletti weir allow for the 
contraction of the water, the quantity of water flowing 
over any portion of the crest is approximately equal to 
that flowing over any other similar portion. Therefore, 
by placing a partition below the weir to divide the crest 
into certain proportional parts, the stream itself is divided 
into similar proportional parts. A beveled board or a 
sharp-edged partition of some kind is placed at right angles 
to the crest and so low as not to interfere with the free 
circulation of air around the jet of water. If the weir 
crest is 3 feet long and a partition is placed 1 foot from 
one end of the crest, the water is divided into two parts, 




Fig. 100. Scale to be screwed on side of Cippoletti weir. This shows at a glance 
the quantity of water passing over the weir. 



356 



IRRIGATION PRACTICE 



one containing one-third and the other two-thirds of the 
whole stream. If the partition is placed l^ feet from the 
end of the crest, the flow is divided into two equal streams. 
This extremely simple method of dividing water seems to 
give general satisfaction. It is frequently desirable to 
have an adjustable divisor to divide a 
certain stream in various ways, at 
various times. Moreover, two or even 
more partitions may be placed below 
the overfall, to divide the flow into 
several streams. (Fig. 101.) 



A„ 



.fv 




1?* 

arvv 



Fig. 101. Divisor attached to Cippoletti weir. 

Frequently, it is necessary to divert a constant quan- 
tity of water from a large canal. For this purpose the 
automatic weir suggested by Winsor probably gives the 
best satisfaction. A board with a long, shallow notch in 
it to act as a spillway is placed lengthwise in the stream 



DUTY AND DIVISION OF WATER 



357 




rufWOUrA»oM£ASUft//VG- W£IR 



Fig. 102. Turnout and measuring weir 



near the head of the secondary ditch to divert a part of 
the water flowing in the main ditch. At the proper distance 
down the secondary ditch an ordinary Cippoletti weir is 
placed. The board containing the spillway notch is raised 
or lowered in accordance with the quantity of water to pass 
over the weir. This device maintains the water flowing 
over the weir at practically the same height, irrespective 
of the quantity of water 
in the main channel. 
(Figs. 102, 103.) 

THE DISTRIBUTION 
OF WATER 



215. Meaning of the 
distribution of water. — 

After the duty of water 
has been decided upon, 
and the quantity of 




Fig. 103. Device for diverting a constant 
quantity of water. 



358 IRRIGATION PRACTICE 

water flowing into the canal and its laterals has been 
carefully measured, there yet remains the perplexing and 
important problem of the proper distribution of the canal 
or reservoir water to the numerous farms of various sizes, 
growing different crops. Each irrigator must receive water 
in a quantity proportional to his interests in the canal, and 
at such a time as will each year insure him a good crop. 
The irrigator, the owner of the water-right, knows only 
one test of the efficiency of the canal management — does 
he have an ample supply of water whenever needed by his 
crops? The success of an irrigation enterprise depends on 
the success with which this test is answered; that is, upon 
the system of distribution of water under the canal. 

216. Methods of distribution. — There are three gen- 
eral methods of distributing irrigation water among 
farmers. First, a continuous flow of water to the farm 
during the whole irrigating season. Second, an inter- 
mittent flow, which means that the farmer gets a certain 
flow of water for a definite length of time at certain inter- 
vals. Third, the delivery of water to the farmer as he 
applies for it. 

Under reservoirs, with an ample supply of stored 
water, any one of these three methods may be used. 
Where canals are taken directly from the rivers the first 
two methods may be used but the third method is prac- 
tically impossible. 

The method chosen for the distribution of water may 
affect greatly the duty of water under the system, for it 
may determine the crops to be grown and the areas to be 
devoted to each. 

217. Continuous flow. — Irrigation is not successful 
unless the head or volume of the irrigation stream is 
sufficiently large to cover quickly a suitable area of land. 



950,000 

900,000 

850,000 

800,000 

750,000 

700,000 

650,000 

600,000 

550,000 

500,000 

450,000 

400,000 

350,000 

h 300,000 

gj 250,000 

^ 200,000 

8 150,000 

Q 100,000 

^ 50,000 




ANNUAL DISCHARGE 

OF STREAM 

4,202,013. 

ACRE FEET 



ACRE FEET 

AVAILABLE FOR 

IRRIGATION BY DIRECT 

DIVERSION 

2,637,094. 

55 PERCENT OF 

ANNUAL FLOW 



ACRE FEET 

WHICH MUST 

BE STORED 

1,564,919. 

45 PERCENT OF 

ANNUAL FLOW 



Fig. 104. The need of storing water in reservoirs. (Yakima River.) 

(359) 



360 IRRIGATION PRACTICE 

If the volume is very small, too large a proportion of the 
water is lost by evaporation during the long time required 
to cover the land with water. The method of continuous 
flow, which means that a stream of the same volume 
enters the farm from the beginning to the end of the irri- 
gation season is successful only if the stream has a suffi- 
cient head, say from 1 to 2 second-feet. If smaller than 
this the method of continuous flow is not usually satis- 
factory. A large farm of from 100 to 300 acres may 
utilize so large a continuous stream. On small farms with 
small water supplies, the method of continuous flow is 
utterly unsatisfactory. A chief objection, even on large 
farms, to the method of continuous flow, is that, under it, 
irrigation must always be going on. The method of con- 
tinuous flow is of real value only when the farm is a mini- 
ature complete irrigation system, representing the diver- 
sity of crops and conditions under the whole canal system; 
for only when this condition exists can the water be used 
to advantage from the beginning to the end of the season. 
There is always more land than water in the irrigated 
sections. A man having a continuous stream of water 
throughout the season would probably plant one-half of 
his farm to grains and other early-maturing crops, and the 
other half to potatoes, beets or other late-maturing crops. 
In the early season the water would be used chiefly on the 
early crops; in the later season on the later crops. By such 
methods, the continuous flow may be made to cover larger 
areas than can the intermittent method. In practice, the 
distribution of water by continuous flow is carried on as 
follows: Ten second-feet are carried by a canal for the 
use of 1,500 acres divided into several farms. Laterals 
are made to each farm, in which is carried the proper pro- 
portion of water for that farm. Thus, a farm of 150 acres, 



DUTY AND DIVISION OF WATER 361 

one-tenth of the total area, would receive a continuous 
flow throughout the season of one-tenth of the total flow, 
or 1 second-foot. A farm of 50 acres, under this system, 
would receive a continuous flow of one-third of a second- 
foot. The system is exceedingly simple after the laterals 
and dividing contrivances have once been established. 
The burden of the method falls upon the farmer who must 
use the water every day and night throughout the season. 

218. Continuous rotation. — The method of distributing 
water by rotation is by far the most satisfactory. In 
America, it was introduced by the irrigation pioneers, 
and since that time has been tried out thoroughly in every 
section of the country. It is the standard method of 
water distribution in Asia, Africa, Europe and Australia. 
Every great irrigation enterprise has either adopted the 
method of rotation or is planning to adopt it. 

By the method of continuous rotation the farmer 
receives a stream carrying a rather large head or volume 
of water for a certain definite number of hours, after 
which no water is at his disposal until his turn comes 
again, when a similar stream is received for the same 
length of time. The relatively large streams of water 
thus supplied give the small farmers the advantage of 
the larger farmers, of applying the water to the land in 
the shortest possible time. Moreover, the farmer is re- 
lieved of the strain of constant irrigation. During the 
time that the stream is at the farmer's disposal, he can 
give himself wholly to the work of irrigation; when that 
work is done, he may turn to some other farm operation. 
Experience has shown this to be most satisfactory to the 
farmer. 

This method tends to eliminate the waste of water. 
Under the method of continuous flow, the steady care of 



362 IRRIGATION PRACTICE 

the water becomes so burdensome that much of the water 
is often allowed to go to waste. The method of rotation, 
on the other hand, develops a spirit of using water care- 
fully, since the time during which it is available for the 
farmer is relatively short and the work must be done at 
that time or not at all until the next turn. The farmer 
under the rotation method receives the water schedule 
early in the spring, and knows in advance the dates on 
which he will receive water. He may then plan much of 
his work for summer, and because of this system can 
make his days more pleasant and profitable. Perhaps the 
greatest argument for the method of rotation is that 
it gives the small farmer an equal chance with the large 
farmer. Under the method of continuous flow the farmer 
owning 10 acres would be obliged to spend as much, or 
possibly more, time in irrigation as would the man who 
owned 100 or more acres. Under the method of continuous 
rotation, the small farmer works as hard as the large 
farmer, during a time in proportion to the acreage that 
he possesses. 

The application of the method of rotation is simple and 
varies only slightly under varying conditions. In the 
main canal, particularly if it is taken directly from the 
river, water flows continuously; and the chief laterals 
likewise carry continuous flows of water. The laterals are 
divided and sub-divided into smaller streams, until the 
quantity of water flowing continuously in each meets 
the requirements of the area of land under the stream, in 
accordance with the duty of water prevailing under the 
system. Let it be assumed that the duty of water under a 
canal system is 100 acres to the second-foot, during the 
irrigation season, and that at each application a depth of 
water not more than 4 inches should be applied. A certain 



DUTY AND DIVISION OF WATER 363 

lateral under this system carries 2 second-feet of water 
continuously, and is, therefore, to be reserved for 200 
acres. This means that the whole 200 acres could be 
covered by this stream, to a depth of 4 inches, every six- 
teen and two-thirds days. In other words, each farm 
under this lateral would receive its allotment of water 
every sixteen and two-third days. If the 200 acres under 
this lateral consist of six farms of 5, 10, 20, 25, 40 and 
100 acres respectively, it may easily be calculated that 
they would receive water every sixteen and two-third 
days as follows: 

Length of irrigation period (every 16 % 
Area of farm days, or 400 hours) 

5 acres 10 hours 

10 " 20 

20 " 40 

25 " 50 

40 " 80 

100 " 200 

200 ** 400 " 

If the stream were larger, the time for each farm would 
be correspondingly decreased. Such a system may be 
followed easily by the water-master and is readily under- 
stood by the farmer. 

Another application of the rotation method is to fill 
the main laterals in rotation. One or a few laterals are 
given all the water of the canal for a certain number of 
days; then another set of laterals, and so on, until the 
rotation has been accomplished. This system is not so 
satisfactory to the farmer as the preceding one, because 
a whole district is for a time without water, when the 
neighboring district has an abundance. Under the first 
system all districts under the canal are at all times doing 
some irrigating, and the presence of the water gives the 
farmer a sense of security. 



364 IRRIGATION PRACTICE 

Still another application of the method of rotation is 
found where city lots are watered for the purpose of main- 
taining home gardens, which usually, because of less care- 
ful cultivation, require water very frequently. Under this 
method the flow of water is divided into many small 
streams that make it possible to irrigate every week or 
every two weeks. 

Each farmer, under the rotation method of distribution, 
is notified at the beginning of the irrigation season of the 
size of the stream allotted, and the time and frequency 
of its use. The farmer is sometimes permitted to turn the 
water into his own ditch at the hour assigned, but the 
better plan is to allow a regularly employed water- 
master or ditch-tender to open or close all gates and to 
divert water to or from farms. The farmers under a 
lateral frequently organize, and as a company manage 
the water from the lateral, exactly as the laterals are 
managed by the canal company. When this is done, the 
responsibility for the ultimate distribution of the water 
rests upon the group of farmers living under the lateral. 
Such lateral organizations are proving very satisfactory, 
and it may be that they will increase until the canal 
managements will need to exercise no further jurisdiction 
over the distribution of water after it has once been 
turned into the laterals. Such a lateral organization 
determines for itself the method of water distribution to 
be used. 

219. Distribution on application. — This method means 
that water flows to a farm only at the request of the 
farmer. The method is practicable only under reservoirs, 
or canals that are always filled with water. Under reser- 
voirs the farmer may be said to own a definite quantity 
of stored water upon which he may draw as he chooses, 



DUTY AND DIVISION OF WATER 365 

just as he does with his money in the bank. The chief 
objection to this method of distribution is that if many 
farmers should call for water at the same time, more 
water might be demanded than the canals could carry. 
When this method is used under ordinary diversion canals, 
it is generally for the purpose of compelling the most 
economical use of water. The tendency of the irrigator to 
use too much water is increased whenever a continuous 
flow of water is supplied, or under methods of rotation, 
when water is given for longer periods than is actually 
needed. If the irrigator feels that he has a limited quantity 
of water in the system, on which he may draw at will, he 
is more likely to practice greater irrigation economy, and 
the surplus water may then be applied beneficially else- 
where. The method of distributing water on the appli- 
cation of the farmer is an ideal system, but of extremely 
limited application. Even under reservoir conditions it 
will probably be found that the rotation method will in 
the end give the greatest satisfaction. 

220. Organization for distribution. — The proper dis- 
tribution of water from great canals can be accomplished 
only by an organization for the purpose. In the early 
irrigation days, when water was relatively plentiful and 
the population small, little attention was given to super- 
vision. Each man drew what he needed from the coopera- 
tive canal. The increasing value of water has made the 
the proper distribution of water more and more important. 
Large canals that serve 3,000 to 20,000 acres, especially, 
are justified in exercising very careful supervision of the 
distribution of the water. It should be insisted upon by 
those who have the best interests of the system at heart. 
Experience points to the conclusion that the success of 
an irrigation system is in direct proportion to the super- 



366 IRRIGATION PRACTICE 

vision given to the distribution of the water and to the 
maintenance of the system. 

Some sort of supervision exists under practically all 
canals, but it is exceedingly varied. Under the Davis and 
Weber Counties Canal in Utah, serving 12,000 acres, divided 
among 520 farmers, four men only are employed to dis- 
tribute the water equitably. Under the Farmers' Canal 
in Montana, serving 15,000 acres, owned by sixty farmers, 
two men on part time supervise the distribution of the 
water. On the other hand, the Gage Canal in California, 
serving only 9,000 acres, finds it profitable to maintain a 
chief engineer and six other men for the proper distribution 
of the water flowing through the canal and for the main- 
tenance of the system itself. The same force of men can 
usually supervise the distribution of the water during the 
irrigation season and maintain the system itself. 

The head of the organization for water distribution 
and canal maintenance, called, possibly, the manager or 
superintendent, should be an irrigation engineer. He 
should be, however, an engineer of a new type — one who 
understands enough of engineering to maintain in a high 
state of excellence the dams, canals, laterals and gates of 
the irrigation system, and who understands enough of 
modern irrigation agriculture to direct the use of the 
water for the production of crops under the canal system. 
To such a man belongs justly the title of irrigation engi- 
neer. If one canal company does not feel itself wealthy 
enough to maintain such a trained superintendent, it is 
often possible for adjoining canal systems to employ the 
same superintendent who can be assisted by water-mas- 
ters from the respective systems. Much money could be 
saved in legal and engineering services if such permanent 
expert help were employed. 



DUTY AND DIVISION OF WATER 367 

This chief worker should be assisted by water-masters 
to whom various duties could be assigned. Some, taking 
the place of the old ditch-rider, should supervise the 
admission of the right quantity of water from the main 
canal into each lateral; others could well be used to 
supervise the up-keep of the main canal and its laterals. 
Ditch-tenders, as assistants to the water-masters, should 
be employed, if necessary, to supervise the farmers' ditches 
drawing water from the laterals. The water-masters and 
the ditch-tenders should be somewhat trained for their 
work. Especially should they understand water units, 
the relation between soils, crops and water, and the 
common methods of measuring and dividing water. 
Moreover, they should be experienced in the practice of 
irrigation so that the farmers' side may be understood 
by them. 

Where the farmers under a lateral have formed a lateral 
organization they could well employ their own water- 
master, who, like the company water-masters, should be 
trained for the work. The day of the untrained man for 
water-distribution has passed. The superintendent, water- 
masters and ditch-tenders, must know their work, and 
must especially be familiar with the use of water in irri- 
gation. Then will the work be done well. 

The cost of such supervision of the distribution of 
water and of the maintenance of the system, including 
the keeping of records, is not great. According to Adams, 
for thirteen of the best-known canals in western America, 
it varies from 9 cents to SI. 30 an acre, with an average 
of 41 3^ cents an acre, a year. This is not at all prohibitive 
if one considers that by the unwise or dishonest distribution 
of water crop failures or crop diminutions may easily 
occur. 



368 IRRIGATION PRACTICE 

221. Regulations and records. — Irrigation under the 
best conditions is complex. If the best results are to be 
obtained from an irrigation system, careful regulations 
must be established and published, and careful records 
must be kept. It is a common fault that the farmers are 
not kept in full touch with the plans under which the 
system is operated, including the duty, measurement 
and distribution of water. Full information concerning 
the rules of the system, including its relation to the 
farmer, should be printed and distributed to every farmer 
under the system. The greater the publicity given the 
operations of the canal management, whether consisting 
of farmers or capitalists, the less friction will accompany 
the work. 

The records of the system should be as orderly as those 
of the best commercial establishments. Water has a de- 
finite cash value; and it should be traced as carefully as 
is any other valuable commodity. At regular intervals 
the flow of water into the main canal and into each of the 
laterals, and as far as possible on to the farms, should be 
carefully measured. Excellent type records may be found 
in Bulletin No. 229 of the Office of Experiment Stations, 
United States Department of Agriculture, entitled 
"Delivery of Water to Irrigators," by Frank Adams. The 
superintendent, water-masters and ditch-tenders should all 
be taught to make such records, and should be charged 
with the duty of making such permanent records. In 
avoiding the characteristic irrigation disputes, such 
records would be of inestimable value. The keeping of 
accurate records by irrigation systems would also help 
greatly to increase the duty of water. Both crop and 
water records should be kept. The want of record-keeping 
is largely responsible for our faulty irrigation methods. 



DUTY AND DIVISION OF WATER 369 

REFERENCES 

Adams, Frank. Delivery of Water to Irrigators. United States 
Department of Agriculture, Office of Experiment Stations, 
Bulletin No. 229 (1910). 

Bark, Don H. Duty of Water Investigations. Ninth Biennial 
Report of the State Engineer of Idaho, 1911-12. 

Buckley, Robert Burton. Facts, Figures and Formulae for Irri- 
gation Engineers (1908). 

Buckley, Robert Burton. The Irrigation Works of India. Second 
edition (1905). 

Carpenter, L. G. On the Measurement and Division of Water. 
Fourth edition. Colorado Experiment Station, Bulletin No. 
150 (1910). 

Cone, V. M. Hydraulic Laboratory for Irrigation Investigations. 
Fort Collins, Colorado. Engineering News, Vol. LXX, No. 10, 
p. 662 (1913). 

Cone, V. M., Trimble, R. E., and Jones, P. S. Frictional Resist- 
ance in Artificial Waterways. Colorado Experiment Station, 
BuUetin No. 194 (1914). 

Flynn, P. J. Irrigation Canals, etc. (1892). 

Horton, Robert E. Weir Experiments, Coefficients and Formulae. 
United States Geological Survey, Water Supply Papers, No. 
200 (1907). 

Lyman, Richard R. Why Irrigation Water Should be Measured. 
Bulletin International Irrigation Congress, Vol. I, p. 63 (1912). 

Lyman, Richard R. Measurement of Flowing Streams. Utah 
Engineering Experiment Station, University of Utah, Bulletin 
No. 5 (1912). 

Lyman, Richard R. Measurement of the Flow of Streams. Proceed- 
ings of American Society of Civil Engineers, Vol. XXXIX, p. 
1913 (1913). 

Mead, Elwood. Irrigation in northern Italy. United States 
Department of Agriculture, Office of Experiment Stations, 
Bulletins Nos. 144 (1904) and 190 (1907). 

Mead, Elwood. Irrigation Institutions. The Macmillan Company 
(1903). 

Newell, F. H. Irrigation. Crowell & Co. (1906). 

X 



370 IRRIGATION PRACTICE 

Tannatt, E. Tappan, and Kneale, R. D. Measurement of Water. 
Montana Experiment Station, Bulletin No. 72 (1908). 

Teele, R. P. Review of Ten Years of Irrigation Investigations. 
United States Department of Agriculture, Office of Experiment 
Stations, Annual Report (1908). 

Teele, R. P. The State Engineer and His Relation to Irrigation. 
United States Department of Agriculture, Office of Experi- 
ment Stations, Bulletin No. 168 (1906). 

United States Reclamation Service. Operation and Mainte- 
nance Use-Book (1913). 

Widtsoe, J. A., and Merrill, L. A. The Yields of Crops with 
Various Quantities of Irrigation Water. Utah Experiment 
Station, Bulletin No. 117 (1912). 

Willcox, William. The Nile Reservoir Dam at Assuan (1903). 

Willcox, William. The Nile in 1904. 1904 (E. & F. N. Spon.) 

Wilson, Herbert M. Irrigation in India. United States Geologi- 
cal Survey, Water Supply and Irrigation Papers, No. 87 (1903). 

Wilson, Herbert M. Manual of Irrigation Engineering. Third 
edition (1899). Wiley & Sons. 

WiNsoR, L. M. Measurement and Distribution of Water. Utah 
Experiment Station, Circular No. 6 (1912). 



V 



CHAPTER XVIII 
OVER-IRRIGATION AND ALKALI 

Over-irrigation and alkali are the two chief evils 
that endanger irrigation as a permanent system of agri- 
culture. These result from the unwise use of water and 
from peculiar soil conditions that may be aggravated by 
excessive irrigation. 

222. Seepage from reservoirs and canals. — Soil is a 
porous mass. Water added to the soil forms a film around 
the soil particles which thickens as more water is added, 
until the film becomes so thick that the liquid water 
slides through the capillary spaces to the greater depths 
of the soil. When the annual rainfall is from 20 to 30 
inches, approximately one-half of it seeps through the 
soil beyond the reach of plants. Under a high rainfall 
more is lost. This seepage continues until the water 
reaches an impervious layer of rock, clay or other sub- 
stance, where a permanent water table is formed; and the 
more water is added from above, the thicker becomes the 
water table. It does not necessarily stand still, but usually 
flows gradually in some direction depending upon the 
inclination of the impervious bottom. According to the 
most recent estimates there is such a layer of water 100 
feet thick, on the average, under the whole surface of the 
earth. 

Much of this subterranean water is derived from the 
rainfall directly; much water seeps also from the river 
beds, which are covered with water practically the whole 

(371) 



372 IRRIGATION PRACTICE 

year. There is always a possibility, also, of seepage from 
reservoirs for the storage of water. If the reservoirs are 
well silted large losses will not occur. A reservoir from 
which a depth of water of not more than 2 feet is lost 
annually is said to be practically impervious. The smaller 
the reservoir, the better silted it is, and, therefore, the 
smaller the loss of water from it. From canals, also, there 
are large losses of water by seepage. For instance, the 
United States Irrigation Investigations have found that, 
as an average for all canals investigated, the loss by seepage 
was 5.77 per cent of the total water carried, for every 
mile of canal. The aggregate loss of water by seepage 
from canals must, therefore, be tremendous. Individual 
canals differ, however, greatly in this respect. In the 
government investigations, the losses from canals varied 
from none to 60 per cent of the total quantity of water 
carried, for each mile of canal. If a canal passes over a 
rocky ledge, much water may be lost through cracks and 
crevices. Canals passing over gravelly soils lose most; over 
sandy soils, nearly as much, and over heavy clay soils, 
least water. New canals always lose more water by 
seepage than do old ones, because silting and settling 
has not been fully established. Small canals lose propor- 
tionately more than large ones, and canals not used in the 
winter lose less than those rilled with water throughout 
the year, although at the time of opening the canals in 
the spring, before silting has gone on, the loss is greater. 
On the average, 30 per cent of the water taken in at the 
head-gates of irrigation canals is lost by seepage from 
the canals themselves. In comparison with this great loss 
all other losses are small. The loss of water by evaporation, 
for instance, is ordinarily less than 15 per cent of the loss 
due to seepage. Carpenter concluded that the water lost 



OVER-IRRIGATION AND ALKALI 373 

from canals in one day is sometimes equivalent to a depth 
of 20 feet and is seldom less than 3 inches over the whole 
canal surface. 

The laterals of canals are subject to similar losses. 
Every irrigation farmer knows that though the flow into 
the lateral at the head-gate may be ample, frequently not 
enough water reaches the farm. Practically, another 
third of the water taken in at the head-gate is gone 
before it reaches the farmer. 

223. Loss from excessive irrigation. — Water is lost 
by seepage on the farm itself, for the common practice is 
to irrigate land too heavily. When more than 5 inches of 
water are added to the soil in any one irrigation, there is 
usually a loss by seepage; yet, on a great many farms, 
twice that much water is applied at one irrigation, pro- 
viding it is available and the soil can be made to absorb 
it. Evil follows such excessive irrigations, especially if 
they succeed each other at short intervals. Farmers who 
misunderstand the use of water usually apply as much as 
possible, as frequently as possible, and urge upon the canal 
managers the necessity of having free access to water. 
An irrigation applied to the soil before the plant roots 
have had time to remove the water added in the previous 
irrigation retards the growth of the crop, and soaks down 
the soil to increase the standing water table. The loss of 
water due to excessive use of the water on the farm is 
often very large. It may safely be estimated that one- 
half of the water taken in at the head-gate of the canal 
is lost by percolation from canals, ditches and excessive 
irrigation. This is an awful waste when the great cost of 
irrigation structures and the vast areas of arid land are 
considered. The old idea that irrigation should take the 
place of tillage must be fought vigorously. 



374 



IRRIGATION PRACTICE 



224. Ground water. — The seepage losses from reser- 
voirs, canals, laterals and farms increase the depth of the 
ground water. Consequently, in irrigated sections, where 
such losses go on uninterruptedly, water rises slowly but 
steadily until wells that were dug 50 to 100 feet deep to 
reach water, now have the water table within 3 to 10 feet 
from the surface. This great layer of ground water flows 
along the impervious layer upon which it rests, usually 



A/»7 




Fig. 105. Rise of ground water from irrigation. 



slowly, but sometimes rapidly. Carpenter found in one 
place that the underground movement of water reached 
a rate of 1 mile an hour. According to the underground 
structure of clay deposits, hardpan or bedrock, this water 
comes out somewhere, usually in the lower-lying lands, to 
form springs, bogs and water-logged lands. The first 
irrigation settlements were often made on the lower lands, 
where the natural seepage made green spots of grass or 
clumps of trees, that looked inviting to the pioneers. As 
the higher-lying irrigation canals were taken out, the 
seepage from them soon converted these green spots, 



OVER-IRRIGATION AND ALKALI 375 

the natural drainage outlets of the district, into water- 
logged lands which had to be abandoned. In that way the 
danger of seepage has from the beginning been called to 
the attention of the irrigation communities. 

True, the water that seeps from the canals and the 
farms is not wholly lost. Some finds its way into the 
lower canals or rivers and is used elsewhere. The "lost 
rivers" of the West are examples of this condition. The 
Sevier River of Utah flows full near its head, and gradually 
disappears until it" is nearly dry; but, lower down, the 
water reappears and the river flows full again. Where the 
underflow can be caught, canals have been built for the 
purpose. Moreover, the underground waters of the 
country, especially in the arid West, will be used more 
and more as irrigation by pumping becomes better under- 
stood. Under the best of conditions, however, much of 
the water that disappears by seepage is permanently 
lost. Seepage must be reduced to the minimum. 

225. Comparison with humid areas. — The danger from 
unnecessary seepage, due to excessive irrigation and canal 
losses, is certainly great; but, the area of resulting water- 
logged lands is not nearly so great in proportion to the 
land surface as are the water-logged lands of humid re- 
gions. According to the last government census, the 
swamp and marsh lands east of the Rocky Mountains, 
subject to reclamation, cover an area of 77,000,000 acres — 
nearly equal to the combined area of Illinois, Indiana and 
Ohio. This area of swamp and marsh land varies roughly 
with the rainfall, which is another proof of the doctrine 
that such lands are determined by the quantity of water 
brought upon the soil surface. The water-logged lands of 
the irrigated regions form a very small fraction of the 
cultivable land, and it lies within the power of the irri- 



376 



IRRIGATION PRACTICE 



gator to reduce this area by wiser methods of conducting 
and using water. 

226. Lined ditches — a remedy. — The chief danger of 
seepage will remain with the canals and laterals, for it is 




Fig. 106. Chain puddler. Used in making canals watertight. 

relatively easy to control the quantity of water used on 
the land. The first obvious remedy against seepage is, 
therefore, to make the ditches more impervious. A canal 
carrying clear water will not of itself become impervious, 
but a canal carrying muddy water will receive the settlings, 
often to such a degree as to reduce or even to stop the 
seepage. Moreover, the leaks due to layers of gravel, sand 
or open rock, over which canals pass, should be stopped 
by the application of clay or some other impervious 
material. Very often, it is advisable to line the whole 
canal with impervious materials or to build flumes or 
pipes to take the place of the canal. The first expense 
seems large, but the annual saving of water and the 



OV RE-IRRIGATION AND ALKALI 



377 



reduction of the area of lower water-logged lands justify 
the expenditure. The many materials used for this pur- 
pose are discussed in special books on the subject. 

The oldest method of lining ditches is by masonry, the 
first cost of which is not, by any means, the most expensive, 
but requires relatively skilled labor, and later considerable 
upkeep. Cement concrete, though it is most expensive, is 
becoming the favorite material for lining ditches, for under 
good supervision, it can be installed rapidly and with 
ordinarily available labor. The great objection to cement 
concrete linings is that in cold districts it is likely to break 
unless carefully covered with earth or sand. Meanwhile 
large, cement-lined canals, even in districts of very cold 
winters, are giving excellent satisfaction. 

Crude mineral oil is also a favorite material for lining 
irrigation ditches. It is heated and while still hot is sprink- 
led with an ordinary road sprinkler over the bottom and 
sides of the canal. It is then harrowed in, usually with a 
chain puddler. This treatment reduces, largely, the 
seepage. The older method of puddling thoroughly the 
bottom and sides of the canal with clay is often the 




Fig. 107. Modified chain puddler. 



378 






IRRIGATION PRACTICE 



cheapest and most satisfactory where the materials are 
near at hand, but the effects are never permanent as 
with masonry or concrete linings. Finally, silting a canal 
is often recommended. Clay or clayey materials, thrown 
into the water at various places, settle wherever the grade 




Fig. 108. Wooden stave pipe carrying irrigation water. 

is not too steep. Afterwards, the silt deposits are puddled 
by the chain puddler. This is a very cheap and often an 
effective method of preventing seepage. (Figs. 106, 107.) 
In California, whole canals have been lined with cement 
concrete, and the definite attempt to reduce seepage by 
first-class canal linings has become established. In other 
states, also, large canals are rapidly being lined. One of 



OVER-IRRIGATION AND ALKALI 



379 



the most notable is the main canal of the Davis and Weber 
Counties Canal Company of Utah, which is lined with 




Fig. 109. Lateral lined witn concrete. 



cement for 10 miles. The work, authorized by farmers 
owning the canal, was done under the direction of some 
of the best engineers of the country. 



OVER-IRRIGATION AND ALKALI 381 

Machines and molds for lining farm ditches are on the 
market and may be obtained at relatively small cost. 
Pipes are often most desirable for the smaller ditches, 
since they eliminate direct loss by evaporation, and also 
the growth of grass or algae near the ditch banks. Smith 
has shown that tile may be made of cement at prices so 
low as to make the method available for the farm irri- 
gation system. The good irrigation farmer should make 
the ditches under his control as impervious as is possible. 

227. The economical use of water — a remedy. — The 
common custom of allowing water to run in irrigation 
canals during the whole year, when it is really needed 
only a few months of the year, is responsible for much 
seepage and positive injury to the lower-lying lands. 
Water, whether taken from reservoir or river, should be 
allowed in the canals only during the seasons of the year 
of actual use. Moreover, on the farm, it should be used 
economically, in harmony with the principles already 
elaborated in this volume. By the more economical use 
of water in these two directions the danger of water-logging 
will be greatly reduced. 

228. Drainage — the final remedy. — Even in the arid 
region, where no irrigation is practised, there will be some 
low-lying wet lands resulting from the natural rainfall 
seeping through the soil from the highlands and the 
river beds. When irrigation is established and practised, 
even under the best conditions, the area of wet land will 
be somewhat larger than it was before. Naturally, the 
best and final remedy for this condition is underdrainage. 
Underdrainage has been well tried out during the last 
hundred years in Europe and in the eastern United States, 
and has been found to be a great and helpful factor in 
making agriculture successful. In spite of the apparent 



382 



IRRIGATION PRACTICE 



paradox, underdrainage on a small scale must be a 
necessary complement of irrigation. The sooner, there- 
fore, that underdrainage is established, in places where it 
is necessary, the better it will be for the development of 
the irrigated region. The low-lying, water-logged lands 
are fertile, and, when drained, require very little irri- 
gation. Many excellent experiments have been made on 




11 



Fig. 111. Pumping plant. (Lifts water 37 feet and 
irrigates 70 acres. (Montana.) 



the underdrainage of lands in the irrigated region, and 
the practice has been found to be wholly successful and 
in cost to be well within the farmer's reach. 

The methods for underdrainage under irrigated con- 
ditions are only slightly different for those prevailing 
under humid conditions. Usually an upper main drain is 
constructed, transverse to the flow from the upper canal, 
so as to intercept the water seeping from above. (See 
Fig. 112.) Where the subsoil rests on a hardpan, blasting 



OVER-IRRIGATION AND ALKALI 



383 



\ 



the impervious layer is often sufficient to improve the 
drainage and to send the obnoxious standing water down- 
ward. It has also been proposed that water-logged lands 
may be drained by pumping, the pumped water to be 
lifted to reclaim lands yet without water. Drainage water 
of the right composition, that is, free from alkali, can 
well be so used, especially in view of the fact that the 
next great development in irrigation, so far as sources of 
water are concerned, will be the use of subsoil water by 
pumping. In Europe, the practice of pumping water for 
the purpose of reliev- 
ing the land from ex- 
cessive moisture and 
of using the pumped 
water, prevails largely. 

Without question, 
underdrainage will 
become an established 
practice in the irriga- 
tion region as it is in 
the humid region. 
The excellent drainage investigations of the Office of 
Experiment Stations of the United States Department 
of Agriculture have collected a great deal of information 
concerning the right methods of draining irrigated lands. 

229. Alkali defined. — Soluble substances are being 
continuously formed in all soils from the progressive 
decomposition of the soil particles. Under high rainfall 
most of these soluble materials are washed into the country 
drainage, and finally into the ocean. It has been suggested 
that the salinity of the ocean is at least in part due to the 
accumulation of salts lost by soils. Under low rainfall, 
which penetrates only a few feet of soil, the soluble 











Fig. 112. Drainage of irrigated lands by inter- 
cepting drains. 



384 IRRIGATION PRACTICE 

constituents remain in the soil and accumulate as the 
years go by. This is one of the characteristic differences 
between the soils of arid and humid regions. These 
accumulations often become so large as to be injurious, 
and then are called alkali. Alkali means the water-soluble 
materials in the soil, especially when the quantity is so 
large as to be injurious to plant-growth. 

Much alkali is of early geological origin. In early 
geological times, as now, large accumulations of soluble 
soil materials occurred in lakes similar to the Great Salt 
Lake or the Dead Sea. When these prehistoric interior 
lakes dried up, there were left behind great deposits of the 
salts held in full or partial solution in the lake water. In 
time these layers of saline materials were covered by silt 
and other materials derived from soils, and thus conserved 
until the present day. When such lands are irrigated the 
water dissolves the soluble salts which may become very 
injurious. 

Ordinarily, alkali appears as an incrustation on the 
soil surface, even on native soils, where conditions are 
favorable to the accumulation of soluble matter. As often, 
however, alkali does not appear as an incrustation, but 
is held in the concentrated soil solution, with equally 
injurious effects. 

230. Seepage and alkali. — Soils tend, naturally, to 
retain their soluble matters, especially those of value in 
plant-growth; but, when a continuous excess of water 
passes through the soil, the soluble substances are given 
up and pass into the country drainage. When such seepage 
water, heavily charged with salts, appears in some low- 
lying place and is evaporated, the alkali is left behind, 
either on the surface or in the remaining soil water itself. 
In either case, the soil becomes increasingly less suitable 



OVER-IRRIGATION AND ALKALI 385 

for plant-production. By over-irrigation, water is lost, 
plant-food is lost, the upper lands are impoverished and 
the lower lands made useless. 

The whole process is well illustrated on a large scale 
by the inland salt lakes, found in abundance over the 
arid region, such as the Great Salt Lake. This lake is, fed 
by the seepage from the neighboring territory, and 
by rivers flowing directly into it. It has no outlet. 
Water is lost from the lake chiefly by evaporation, 
and the soluble substances carried by the water entering 
the lake are accumulated in the lake water. As a result, 
the water has become so saturated that crystallization is 
going on. On a smaller scale, in every valley bottom with 
poor drainage, the process is being repeated. Large 
areas have thus been and are being made alkaline. 

231. Upward leaching. — Another phase of the alkali 
question does not concern itself with seepage. Arid 
soils are rich in soluble matters, which, when evenly 
distributed throughout the soil, are advantageous in 
plant-growth. If by any chance the soluble substances of 
the upper 6 to 10 feet of the soil are partly concentrated 
near the surface, plant injury is almost sure to follow. 
Such concentration frequently occurs under irrigation. 
Water, added to the soil in moderation moves downward 
only a few feet, but in its descent dissolves some of the 
water-soluble soil constituents. By transpiration and 
evaporation the water thus added moves upward and 
carries with it the substances dissolved in its descent. At 
the soil surface, the water evaporates and the salts are left 
behind. As this is continued, the soluble soil constituents 
tend to accumulate at or near the surface. This process 
has been named upward leaching. It is a condition that 
need not cause permanent injury, for it may be controlled. 

Y 



386 



IRRIGATION PRACTICE 



The process has gone on in nature for many ages; the 
salts have each year been washed down to a depth ordi- 
narily reached by the rainfall and returned to the surface 
during the warmer season. Arid soils are often underlaid 
at a certain depth by layers of salts which indicate the 




Fig. 113. Structure of an alkali spot. 



annual penetration of the rainfall throughout the ages 
before man began to cultivate the soil. (Fig. 113.) 

Upward leaching may be prevented by preventing 
evaporation from the soil surface. The tillage methods 
recommended for the conservation of water are those 
that will prevent the accumulation of alkali at the soil 
surface. 



OVER-IRRIGATION AND ALKALI 387 

232. Use of saline water. — Another source of alkali is 
the use of water charged with large quantities of soluble 
salts. As shown in Chapter V, all natural waters contain 
certain quantities of dissolved substances. Only when the 
proportion of such soluble salts is too large does there 
appear to be any danger in the use of such waters. In 
fact, saline waters have usually been undervalued for 
purposes of irrigation. 

Plants can tolerate large quantities of soluble salts in 
irrigation water providing they are of the right mixture. 
Thus Kearney and Cameron found that seventy parts of 
magnesium sulphate in 1,000,000 parts of water repre- 
sented the highest concentration in which plant-roots 
could survive; yet, in the presence of a concentrated 
solution of calcium sulfate, 33,600 parts of magnesium 
sulphate in 1,000,000 parts of water could be tolerated. 
Gypsum and common salt are both antidotes for mag- 
nesium sulfate; magnesium carbonate is an antidote for 
sodium carbonate and sodium chloride, raising their limit 
two to four times; lime is an antidote for magnesium and 
sodium, in the form of sulfates, carbonates or chlorides, 
raising the limit of these dangerous salts hundreds of 
times. Kearney found that the native irrigationists of 
northern Africa raised successfully many of the ordinary 
crops with water containing 8,000 parts of soluble salts 
for each 1,000,000 parts of water. Hilgard, as a result 
of his long life of experimentation on such subjects, holds 
that from 1,200 to 1,700 parts of soluble matters in each 
1,000,000 parts of water represent the highest limit of 
endurance for ordinary plants. This, however, is much 
lower than that observed by Kearney in northern Africa, 
or observed by other students in other parts of the world. 
The concentration of water that may be used for irrigation 



388 IRRIGATION PRACTICE 

purposes depends primarily upon the proportions of the 
salts in the water. The poisonous action of irrigation 
water is not the sum of the poisonous actions of its various 
constituents; for, as observed, the effect of any compound 
is qualified by the presence of other compounds. The whole 
subject is in a confused state and needs extensive in- 
vestigation. 

The real danger in the use of saline waters for irriga- 
tion, whether they contain 1,000 or 8,000 parts of soluble 
matter to 1,000,000 parts of water, is in the residue of 
salts from the evaporated matter. For example, if an 
irrigation water contains 1,000 parts of soluble matter 
in each 1,000,000 parts of water, and if 18 inches of this 
water are used over an acre each year, 4,000 pounds of 
alkali an acre are added each year. As this is repeated 
year after year, the accumulation of salts becomes so 
great as to render the land unfit for farming. To over- 
come this difficulty it is necessary, when saline waters are 
employed in irrigation, to reverse the usual rule, and to 
use quantities of water so large that drainage is assured. 
The excess of salt is then washed into the country drain- 
age, and alkali accumulations are prevented. Such hand- 
ling of saline waters is, however, dangerous in that the 
excess of water, heavily alkaline, may appear on the 
lower lands, there to cause injury. Before saline waters 
are used for irrigation, they should be investigated care- 
fully as to their composition and their probable effect 
on the land. 

233. Alkali deposits. — The great deposits of alkali or 
alkali impregnated soils and rocks common to arid 
countries are another source of alkali ._ These deposits, 
yet to be studied exhaustively, are associated with the 
geological history of the country. In early geological 



OVER-IRRIGATION AND ALKALI 



389 



days, salt lakes, similar to the Great Salt Lake, were no 
doubt formed, which were dried by the changing climate, 
leaving great masses of salt, that were later covered by 
washings from the hills. In other cases, silt and other 




Fig. 114. Quaternary Lakes of the Great Basin. Sources of alkali deposits. 

soils of early geological days were deposited in the presence 
of salt or brackish water. These in time became hardened 
into rocks. Consequently, over much of western America 
there are great exposures of shales and sandstones con- 
taining large percentages of water-soluble substances. 



390 IRRIGATION PRACTICE 

On the soils derived from many of these deposits, plant- 
growth is difficult or impossible, and they are therefore 
easily recognized. 

Water passing through these alkali deposits of early 
times and dissolving the salts, carries alkali to otherwise 
alkali-free sections. This is a chief source of alkali, next 
in importance to over-irrigation, although it has been 
largely overlooked by students of alkali. Knight and 
Slosson, of Wyoming, have shown that great numbers of 
such deposits occur in Wyoming; other students of 
western conditions have discovered similar deposits in 
various districts; and Stewart and Peterson, of Utah, 
have recently confirmed the wide distribution of such 
alkali deposits. Once the existence of such deposits is 
recognized in the neighborhood, precautions against them 
may be taken, and they need not then be a menace. 
(Fig. 114.) 

234. Kinds of alkali. — Since alkali is simply the 
soluble matter of soils accumulated to an injurious degree, 
it follows that alkali may contain any or all of the con- 
stituents of rocks and soils. The numerous existing analy- 
ses show that in alkali there is a preponderance of the 
bases, sodium, calcium and magnesium, combined with 
hydrochloric, sulfuric, carbonic and nitric acids. In 
other words, the chlorides, sulfates, carbonates and 
nitrates of sodium, calcium and magnesium are the chief 
constituents of ordinary alkali. In addition to these 
dominant constituents there are a great many others, as 
potassium salts, phosphates and other indispensable 
plant-foods. Alkali may be said to be the cream of soil 
fertility, so concentrated as to cause plant indigestion. 
The following table gives partial analyses of four samples 
of alkali crust: 



OVER-IRRIGATION AND ALKALI 



391 



Percentage Composition of Alkali Crusts 



Sodium carbonate (sal- 
soda) 

Sodium chloride (common 
salt) 

Sodium sulfate (Glau- 
ber's salt) 

Sodium nitrate (niter) 

Magnesium sulfate (Ep- 
som salts) 

Calcium sulfate (gyp- 
sum) 



New 
Mexico 



Trace 

3.2 

70.4 
Trace 

3.2 

11.8 



Wyoming 



Trace 

1.9 

39.7 
Trace 

42.4 

3.6 



Utah 



2.0 

1.4 

3.2 
Trace 



90.3 



Colorado 



40.8 



30.5 



Utah 



88.6 



In the first sample from New Mexico, sodium sulfate, 
or Glauber's salt, predominates; in the second, from 
Wyoming, magnesium sulfate, or Epsom salts, is most 
prominent; in the third, from Utah, calcium sulfate, or 
gypsum, predominates; in the fourth, from Colorado, 
sodium nitrate, or niter, predominates, and in the fifth, 
from Utah, sodium chloride, or common salt, predom- 
inates. 

Between the extreme compositions shown in the above 
table, all possible variations occur. It is impossible to 
lay down any rule for the composition of alkali, unless 
the source is known. The following analysis of a Cali- 
fornia sample also shows the complex composition of 
alkali : 

Potassium sulfate 3.95 

Sodium sulfate 25.28 

Sodium nitrate 19.78 

Sodium carbonate 32.58 

Sodium chloride 14.75 

Sodium phosphate 2.25 

Ammonium carbonate 1.41 

Total 100.00 



392 



IRRIGATION PRACTICE 




Ordinarily, alkali is classified as white, black or brown. 
Black alkali appears as a black, shiny mass, or as black 
spots, over the soil. White alkali has a clean, white appear- 
ance like that of salt. Experience has demonstrated that 
black is far more injurious than white alkali, for it is 
corrosive and girdles the tissues of the plant near the 
soil surface and thus destroys the plant itself. White 
alkali is relatively harmless, and injures plants only as it 

is present in too 
large an abun- 
dance. Black or 
brown alkali is 
composed chiefly 
of the carbonate 
or nitrate of 
sodium, with 
perhaps some 
common salt. 
The carbonate dissolves the plant tissues with the for- 
mation of a black mass; it moreover destroys the tilth of 
the soil by destroying its structure. The nitrate forms 
brown spots; it also makes soils mushy; but, when the 
soils containing nitrates dry out, a very characteristic 
crumbly soil results. The white alkali is composed of 
the sulfates and chlorides of sodium, calcium and 
magnesium. 

235. Tolerance for alkali. — The tolerance for alkali of 
plants depends on five factors: (1) the main salt, (2) 
the concentration, (3) the associated salt, (4) the age of 
the plant, and (5) the plant itself. Kearney and Cameron, 
experimenting with seedlings of various plants, have 
shown that various salts affect growth variously. Sodium 
carbonate is the most injurious constituent of alkali, 



Fig. 115. Effect of a strong solution of potassium 
nitrate on protoplasm. 



OVER-IRRIGATION AND ALKALI 



393 



followed by sodium chloride, followed by sodium sulfate, 
followed by magnesium sulfate. This is the general order 
of tolerance of these four important salts, frequent con- 
stituents of alkali. 

The injury from each salt depends upon the mixtures 
of salts in the alkali. The action of magnesium sulfate 
is almost wholly destroyed, if there is mixed with it a 
quantity of calcium sulfate. In fact, calcium sulfate is 
the great neutralizer of the dangerous substances of 




Fig. 116. Vegetation on alkali lands. California. 

ordinary alkali. The salts found in alkali do not show 
any specific effect upon the wilting coefficient. Any 
of the alkali salts, present in large quantity, tends to 
increase the water-cost of dry matter. Evaporation from 
alkali soils is always reduced. In general, while alkali tends 
to reduce the direct evaporation from the soil, it also tends 
to increase the water-cost of dry matter. 

The concentration of alkali in the soil that will injure 
plants has not been finally determined. Most work on the 
subject has been done by Hilgard and Loughridge of 
the University of California. Loughridge has tabulated 
the highest quantity of alkali salts endured by various 



394 



IRRIGATION PRACTICE 



crops, as based upon many years of observation at the 
California stations. In the following table will be found 
the information given by Loughridge, adapted slightly: 

Highest Quantity of Alkali Salts Endured by Various Crops 

Fruit Trees 



Per cent of 
sodium sulfate (Glau- 
ber's salt) in soil 



Grapes 0.25 

Figs 68 *':::::: }°- 2 °-° 15 

Almonds } 

Oranges [-0.15-0.10 

Pears ) 

Apples \ 

Peaches >0. 10-0.05 

.Prunes I 

Apricots / 



Per cent of sodium 

chloride (common salt) 

in soil 



Grapes 0.062 

Olives ^ 

0range , s VO.05-0.01 

Almonds I 

Mulberry / 

Pears 

Apples 

Prunes 

Peaches \ 0.01-0.005 

Apricots. . . . 

Lemons 

Figs 



Per cent of 
sodium carbonate (sal- 
soda) in soil 



Grapes ^ 

°™nges V .005-0.001 

Olives ( 

Pears / 

Almonds ) 

Prunes V0.CC10-C.0005 

Figs ) 

Peaches 

Apples 

Apricots ^-0.0005-0.0001 

Lemons 

Mulberry. . . 



Small Cultures 



Per cent of 
sodium sulfate (Glau- 
ber's salt) in soil 



ittloidV.:! - 75 - - 50 



Hairy vetch 

Sorghum 

Sugar beets . . 
Sunflower. . . . 

Radish 

Salt-grass 

Artichoke 

Carrot 

Gluten wheat. 

Wheat 

Barley 

Goat's rue.. . . 
Alfalfa 

(young) 

Rye 

Canaigre 

Rye-grass 

Modiola 

Bur clover . . . 

Lupine 

White melilot . 
Celery 



.0.50-0.25 



^0.25-0.10 



•0.10-0.05 



)■ 0.05-0.01 



Per cent of sodium 

chloride (common salt) 

in soil 



Salt-grass 0.43 

Modiola 0.25 

Saltbush ^ 

Sugar beets. 
Sorghum. . . . 

Celery 

Onions ^ 

Potatoes 

Sunflower. . . . 

Barley 

Hairy vetch . 

Lupine 

Carrot 

Radish 

Rye 

Artichoke. . . . 
Gluten wheat 

Wheat 

Grasses 

White melilot 
Goat's rue. . . 
Canaigre 



0.10-0.05 



^ 0.05-0.01 



0.010-0.005 



!»• 



0025-0.0005 



Per cent of 
sodium carbonate (sal- 
soda) in soil 



Salt-grass 

Saltbush 

Barley 

Bur clover. . . . 

Sorghum 

Radish 

Modiola 

Sugar beets . . . 
Gluten wheat . 

Artichoke 

Lupine 

Hairy vetch.. . 

Alfalfa 

Grasses 

Kafir corn .... 
Sweet corn . . . 

Sunflower 

Wheat 

Carrots 

Rye 

Goat's rue. . . . 
White melilot. 

Canaigre 

Salt-grass 



.0.84 
.0.12 



>0.075-0.050 
} 0.050-0.025 

, 0.025-0.010 

VO.010-0.005 
[ 0.005-0.001 



OVER-IRRIGATION AND ALKALI 395 

For fruit trees, the tolerance of Glauber salts varies 
from 0.25 to 0.025 of 1 per cent; of common salt from 
0.062 to 0.005 of 1 per cent; of sal-soda from 0.005 to 
0.0001 of 1 per cent. For the small cultures, tolerance of 
Glauber's salt, as of salt and sal-soda, is increased con- 
siderably. However, the variation for various crops in 
the table is so great as to make it practically impossible 
to lay down any definite rules that may be generally used 
in agriculture. Loughridge concludes that, in general, for 
fruit trees, the maximum tolerance of alkali in the soil 
ranges from 0.28 per cent to 0.04 per cent; for small 
cultures, excluding the salt bushes, from 1.0 per cent to 
0.06 per cent. 

The experience of the Bureau of Soils is perhaps the 
best for formulating limits of the tolerance of plants for 
alkali. The staff of the Bureau of Soils has investigated 
practically every important alkali area of the United States. 
They have had ample opportunity to correlate the 
growth on the soil with the alkali content. It has been 
found that on land containing, to a depth of 6 feet, 
up to 0.2 per cent of total alkali, none of the common 
crops are injured, unless carbonates greatly predominate, 
or unless most of the salt is concentrated in the upper 
part of the first foot. On land containing from 0.2 per 
cent to 0.4 of total alkali, or from 0.05 to 0.1 per cent of 
black alkali, or 0.5 per cent of sodium chloride, or 1 per 
cent of sodium sulfate, all but the most sensitive crops 
will grow. Near the higher limits, all but the most resis- 
tant crops show signs of distress. A grade of land contain- 
ing from .4 to .6 per cent of total alkali and from .1 to .2 
of black alkali contains a little too much for common 
crops. Pastures usually grow on such land. Where the 
land contains from .6 to 1 per cent of total alkali it is 



396 



IRRIGATION PRACTICE 



almost worthless for general or fruit farming. In spite, 
however, of these well-established limits, it is known that 
even with 3 per cent of alkali in the upper 6 feet, crops 
may occasionally be grown successfully. Much depends, 
as already said, upon the crop, the nature of the alkali, 
the nature of the soil, methods of irrigation, and tillage. 




Fig. 117. Alkali spots on irrigated pasture. 

The crop itself determines, fundamentally, the tolerance 
for alkali. Certain fruits and small crops endure large 
quantities of alkali, while others are very sensitive to it. 
When properly cultivated, kafir corn, sorghum, sugar 
beets, and barley are excellent alkali-resistant crops. 
The date palm, in its resistance to alkali, stands at the 
very head of cultivated crops. However, the area over 
which this plant may be grown at present is relatively 
small. 



OVER-IRRIGATION AND ALKALI 397 

The age of the crop also determines largely the tol- 
erance of alkali. Germinating crops can stand only small 
quantities of alkali; but as they become older and the root- 
system better established the tolerance increases. There- 
fore, it is advisable to wash the alkali far down into the 
subsoil at the time of seeding, so that germination and 
first growth may occur without hindrance. The quality 
of crops is often reduced by the presence of alkali. 
Headden found that the quality of beets was largely 
interfered with by the presence of nitrates in the soil. 

All in all, the subject of the tolerance of plants for 
alkali is in considerable confusion. This exceedingly 
difficult subject needs to be worked over, with new 
experiments and devices before the last word concerning 
it can be spoken. 

236. Cropping against alkali. — Apparently the sim- 
plest method of utilizing alkali lands is to grow upon 
them alkali-resistant plants. Many native plants thrive 
on alkali lands, and are relatively sure indicators of alkali 
conditions. Greasewood, shad-scale, salt-weeds and salt- 
bushes thrive best on lands that are fairly rich in alkali. 
While these plants usually grow on alkali soils they often 
do well on alkali-free soils, and are not therefore invariable 
indicators of alkali. Unfortunately, most of the native 
alkali-resistant plants have little agricultural value. They 
are usually unpalatable and of low digestibility and 
feeding value. There are a number of cultivated plants 
that also endure alkali. Among these is the Australian 
salt-bush, tried out in California, which yields well and 
makes a fairly palatable forage. Sweet clover, which 
is almost a weed in many localities, grows remarkably 
well on certain classes of alkali land, and, if cut early, 
forms a palatable stock-feed. Lucern once started on 



398 IRRIGATION PRACTICE 

alkali land, does fairly well, as do also sugar beets, sorghum, 
kafir corn, rye, the date palm, grape-vines and many 
other crops which yield annual crops of fair size in the 
presence of relatively large quantities of alkali. 

The theory of reclaiming alkali lands by cropping is 
that each crop absorbs from the soil considerable quan- 
tities of alkali, and as cropping is continued year after 
year, there is diminution in the alkali content of the soil 
corresponding to the quantities removed by the crops. 
The Australian salt-bush, containing about 20 per cent 
of ash, may yield five tons an acre, which means each 
crop removes from the soil about one ton of alkali. This, 
continued for several years, would tend to make an alkali 
soil better capable of producing ordinary crops. 

On alkali soils, deep-rooted plants do better than 
shallow-rooted plants, and leafy plants do better than 
those giving less shade. Legumes do not resist alkali well, 
while the sunflower family does exceedingly well in the 
presence of alkali. The fiber plants, such as flax, are 
sensitive to alkali. Much information is yet needed con- 
cerning alkali-resistant plants; the conditions under 
which they thrive best, and the degree to which they are 
able to remove alkali. Much new work can profitably be 
done on this branch of the subject of alkali. 

237. Chemical treatment for alkali. — The suggestion 
has been made repeatedly that something might be added 
to the soil to neutralize alkali. The chemical nature of 
the constituents of alkali makes it difficult to make them 
insoluble or to change them into something less obnoxious. 
The conclusion has been reached, after much experi- 
mentation, that only sodium carbonate may be corrected, 
practically, by chemical treatment. Hilgard demon- 
strated many years ago, on the California experimental 



OVER-IRRIGATION AND ALKALI 399 

farms, that calcium sulfate, or gypsum, added to a soil 
containing sodium carbonate, changed the carbonate to 
a sulfate; that is, gypsum changed black alkali to white 
alkali. Twice as much gypsum as there is sodium car- 
bonate in the soil, should in time be worked into the soil 
thoroughly. To add 200 to 400 pounds of gypsum an 
acre annually, is better than to attempt to add the full 
quantity all at once. After each treatment the soil should 
be irrigated. This is an excellent corrective for black 
alkali; and it is, indeed, the only known chemical cor- 
rective for alkali. 

238. Scraping the surface. — Another method of com- 
bating alkali is to allow evaporation to go on until the 
alkali has crusted the soil surface, and then to scrape off 
this crust and to remove it permanently from the soil. By 
this method, hundreds of pounds of alkali per acre may 
be removed from the soil; but not enough is carried off 
really to improve the soil, and the labor involved is so 
large as to make the whole process of doubtful value. 

239. Tillage against alkali. — Alkali is most injurious 
if concentrated near the surface. If distributed evenly 
throughout the soil relatively large quantities of alkali 
may be endured by plants. This condition may be secured, 
measurably, by reducing evaporation and thereby pre- 
venting the rise of alkali. This is a very effective method 
of preventing damage from alkali. Orchards seriously 
injured by alkali have frequently been restored to a 
profitable condition by thorough cultivation. The com- 
mon custom is to plow under the crust, irrigate thoroughly, 
and follow this by a thorough cultivation as often as 
needs be throughout the season. Alkali lands should also 
be cultivated in the spring, when evaporation is likely to 
go on rapidly. 



400 IRRIGATION PRACTICE 

240. Washing out alkali. — In the attempt to remove 
alkali, lands are often flooded with a large quantity of 
water flowing under a high head. The theory has been 
that the rapidly moving water passing over the soil will 
dissolve the alkali and carry it off. This, however, has 
been found to be ineffective, for, the moment the water 
dissolves the alkali, it sinks into the soil and only the pure 
water runs off the surface. 

A better method is to apply irrigations so large that 
the water seeps into the country drainage. When this 
can be done it is very satisfactory, but only on naturally 
well-drained lands, or on open soils, can it be made 
effective. Occasionally, the soil is underlaid by a hard- 
pan, and it is found helpful to' make holes through this 
impervious layer to connect with the more permeable soil. 
In any case, when much water is used on alkali land, irri- 
gation should be followed by careful cultivation. 

241. Underdrainage the final remedy. — The only 
really satisfactory treatment for alkali is one that removes 
the alkali permanently from the soil. This is accomplished 
best by underdrainage, since few soils permit of natural 
drainage. 

The feasibility of underdrainage has been demon- 
strated in all parts of the world, and the only consider- 
ations, with respect to alkali lands, are the cost of instal- 
lation and the disposition of the drainage water. The cost 
is no higher in irrigated than in humid regions; and irri- 
gated lands are fully as valuable as those in humid regions. 
The disposition of the drainage water depends on local 
conditions, and must be carefully determined upon, for 
the drainage from alkali lands is unfit for agricultural 
uses. Drainage from such lands need not, however, be 
continuously great, for lands, underdrained for the re- 



OVER-IRRIGATION AND ALKALI 401 

moval of alkali, are not necessarily swampy; on the 
contrary, they may be perfectly dry in their natural 
condition. 

If underdrainage is used as the final remedy for alkali, 
very heavy applications of water must be applied for 
some time, until the alkali is thoroughly washed out and 
carried off through the drains. This is a dangerous 
procedure, for valuable plant-foods are taken out with the 
alkali. The washing of the soil should be stopped, there- 
fore, as soon as the main alkali condition has been cor- 
rected. 

The possibility of removing alkali by underdrainage 
has been well demonstrated by the Bureau of Soils of the 
United States Department of Agriculture. The pioneer 
experiment was made on land located west of Salt Lake 
City, toward the Great Salt Lake. The farm, when 
located, was covered with a glistening coat of white 
alkali. The soils of the district are generally heavily 
impregnated with alkali, chiefly common salt, from the 
concentrated water of the Great Salt Lake, which has 
either overflowed in the past, or has moved through the 
subsoil. From 2 3^ to 5 per cent of alkali was found in the 
soil at the time the experiments began, and ground water 
stood about 4 feet from the surface. Tile pipe was laid 
in the usual manner, at a cost of about $16 an acre. In 
1903, the year after the laying of the tile, the land was 
thoroughly flooded, and from August, 1904, it was again 
flooded thoroughly, at various intervals, until 1906, when 
the land was returned in a good agricultural condition to 
the owner. Since that time a thrifty crop of alfalfa has 
grown upon it, as proof that the alkali condition has been 
permanently corrected. From September, 1902, to Octo- 
ber, 1904, the water added was equal to a little more 
z 



402 IRRIGATION PRACTICE 

than 10 feet in depth over the whole area. This quantity 
of water carried off 5,317 tons of salt, and reduced the 
alkali content to 13 per cent of what it was at the beginning 
of the experiment. Not only was this tract of 40 acres 
reclaimed by this treatment, but the beneficial effects of 
the drainage were felt in the adjoining fields. 

At Fresno, California, where the predominating type 
of alkali was a mixture of the chloride and the carbonate 
of sodium, a hopelessly alkaline tract was restored by tile 
drainage in less than one year to permanent fertility. At 
Billings, Montana, where the prevailing type of alkali 
was sodium sulphate, similar reclamation work was 
accomplished in two years. These three experiments, 
at Salt Lake City, Fresno, and Billings, representing the 
three chief types of alkali, demonstrate the feasibility of 
reclaiming alkali lands by under drainage, provided there 
is a sufficient fall of the land and a suitable outlet. 

Alkali may attack and injure the materials of which 
the drains are made. When glazed pipe is used, the danger 
is small; but if concrete or cement pipe is laid, the danger 
is large, for alkali uniting with the calcium hydroxide 
of the cement tends to disintegrate concrete. In the de- 
structive action on concrete, sodium sulfate stands first, 
followed by magnesium sulfate and then by sodium 
carbonate. Sodium chloride has a small but definitely 
injurious effect. 

Alkali lands represent only a small proportion of the 
total irrigated area. Cautious irrigation of the higher- 
lying lands will prevent the increase of this area, and 
underdrainage will reduce it considerably. With our pres- 
ent knowledge, there is no reason why the "alkali plague" 
should be feared. Vigorous measures should be taken, 
however, if the alkali trouble is approaching. 



OVER-IRRIGATION AND ALKALI 403 

REFERENCES 

Bonsteel, Jay A. Marsh and Swamp Lands. United States 

Department of Agriculture, Bureau of Soils, Circular No. 69 

(1912). 
Brown, Charles F. Drainage of Irrigated Lands. United States 

Department of Agriculture, Farmers' Bulletin No. 371 (1909). 
Brown, Charles F., and Hart, R. A. The Reclamation of Seeped 

and Alkali Lands. Utah Experiment Station, Bulletin No. Ill 

(1910). 
Burke, Edmund, and Pinckney, Reuben M. The Destruction of 

Hydraulic Cements by the Action of Alkali Salts. Bulletin 

No. 81 (1910). 
Carpenter, L. G. Seepage or Return Waters from Irrigation. 

Colorado Experiment Station, Bulletin No. 33 (1896). 
Carpenter, L. G. The Loss of Water from Reservoirs by Seepage 

and Evaporation. Colorado Experiment Station, Bulletin No. 

45 (1898). % 
Carpenter, L. G. Losses from Canals from Filtration or Seepage. 

Colorado Experiment Station, Bulletin No. 48 (1898). 
Dorsey, Clarence W. Alkali Soils of the United States (contains 

United States literature). United States Department of Agri- 
culture, Bureau of Soils, Bulletin No. 35 (1906). 
Dorsey, Clarence W. Reclamation of Alkali Land in Salt Lake 

Valley, Utah. United States Department of Agriculture, 

Bureau of Soils, Bulletin No. 43 (1907). 
Dorsey, Clarence W. Reclamation of Alkali Soils at Billings, 

Montana. United States Department of Agriculture, Bureau 

of Soils, Bulletin No. 44 (1907). 
Elliot, C. G. Development of Methods of Drainage for Irrigated 

Lands. United States Department of Agriculture, Office of 

Experiment Stations, Annual Report for 1910. 
Elliot, C. G. Drainage of Farm Lands. United States Depart- 
ment of Agriculture, Farmers' Bulletin No. 187 (1904). 
Etcheverry, B. A. Increasing the Duty of Water. California 

Experiment Station, Circular No. 114 (1914). 
Fleming, B. P. Seepage Investigations. Wyoming Experiment 

Station, Bulletin No. 61 (1904). 
Fitterer, J. E. Reclamation by Drainage. Wyoming Experiment 

Station, Bulletin No. 90 (1911). 



404 IRRIGATION PRACTICE 

Fuller, Myron L. Summary of the Controlling Factors of Artesian 

Flows. United States Geological Survey, Bulletin No. 319 

(1908). 
Fuller, Myron L. Underground Waters for Farm Use. United 

States Geological Survey, Water Supply Papers No. 255 (1910). 
Fortier, Samuel, and Cone, Victor M. Drainage of Irrigated 

Lands in the San Joaquin Valley, California. United States 

Department of Agriculture, Office of Experiment Stations, 

Bulletin No. 217 (1909). 
Headden, W. P. The Fixation of Nitrogen in Some Colorado Soils. 

Colorado Experiment Station, Bulletins Nos. 155, 178 and 186 

(1913). 
Headden, W. P. Deterioration in the Quality of Sugar Beets, Due 

to Nitrates Formed in the Soil. Colorado Experiment Station, 

Bulletin No. 183 (1912). 
Headden, W. P. Destruction of Concrete by Alkali. Colorado 

Experiment Station, BuUetin No. 132 (1908). 
Hilgard, E. W. Soils. The Macmillan Company (1906). 
Kearney, Thomas H. The Wilting Coefficient for Plants in Alkali 

Soils. United States Department of Agriculture, Bureau of 

Plant Industry, Circular No. 109 (1913). 
Kearney, Thomas H., and Harter, L. L. Comparative Tolerance 

of Various Plants for the Salts Common in Alkali Soils. United 

States Department of Agriculture, Bureau of Plant Industry, 

BuUetin No. 113 (1907). 
Loughridge, R. H. Tolerance of Eucalyptus for Alkali. California 

Experiment Station, Bulletin No. 225 (1911). 
Machie, W. W. Reclamation of White-Ash Lands Affected with 

Alkali at Fresno California. United States Department of 

Agriculture, Bureau of Soils, Bulletin No. 42 (1907). 
Mead, Elwood. Report of Irrigation and Drainage Investigations, 

1904. United States Department of Agriculture, Office of 

Experiment Stations, Annual Report for 1904. 
Mead, Elwood, and Etcheverry, B. A. Lining of Ditches and 

Reservoirs to Prevent Seepage Losses. California Experiment 

Station, Bulletin No. 188 (1907). 
Means, Thomas H. Reclamation of Alkali Lands in Egypt. United 

States Department of Agriculture, Bureau of Soils, Bulletin 

No. 21 (1903). 



OVER-IRRIGATION AND ALKALI 405 

Schlichter, Charles S. The Rate of Movement of Underground 
Waters. United States Geological Survey, Water Supply- 
Papers, No. 140 (1905). 

Smith, G. E. P. Cement Pipe for Small Irrigating Systems and 
Other Purposes. Arizona Experiment Station, Bulletin No. 55 
(1907). 

Stewart, Robert, and Greaves, J. E. The Movement of Nitric 
Nitrogen in Soil and Nitrogen Fixation. Utah Experiment 
Station, Bulletin No. 115 (1911). 

Tannatt, E. Tappan, Anderson, A. P., and Kneale, R. D. Seepage 
and Drainage. Montana Experiment Station, Bulletin No. 65 
(1907), and No. 76 (1909). 

Tannatt, E. Tappan, and Burke, Edmund. The Effect of Alkali 
on Portland Cement. Montana Experiment Station, Bulletin 
No. 68 (1908). 

Teele, R. P. Review of Ten Years of Irrigation Investigations. 
United States Department of Agriculture, Office of Experi- 
ment Stations, Annual Report for 1908 (separate). 

Teele, R. P. Losses of Irrigation Water and Their Prevention. 
United States Department of Agriculture, Office of Experi- 
ment Stations, Annual Report for 1907. 

Talmage, J. E. The Great Salt Lake, Present and Past (1900). 

True, Rodney H., and Bartlett, Harley, Harris. Absorption 
and Secretion of Salts by Roots as Influenced by Cultural 
Solutions. United States Department of Agriculture, Bureau 
of Plant Industry, Bulletin No. 231 (1912). 

Widtsoe, J. A., and Stewart, Robert. The Soil of the Southern 
Utah Experiment Station. Utah Experiment Station, Bulletin 
No. 121 (1913). 

Woodward, S. M. Land Drainage by Means of Pumps. United 
States Department of Agriculture, Office of Experiment Sta- 
tions, Bulletin No. 243 (1911). 

Wright, J. O. Swamp and Overflowed Lands in the United States. 
United States Department of Agriculture, Office of Experi- 
ment Stations, Circular No. 76 (1907). 



CHAPTER XIX 
IRRIGATION IN HUMID CLIMATES 

Irrigation should always be practised to supplement 
the natural rainfall. Where there is much rainfall, either 
during the growing season, or in the winter, that can be 
stored, less irrigation is needed than where the rainfall is 
low. Wherever the rainfall is not high enough to yield 
maximum crops, however, irrigation is desirable; and 
wherever the rainfall does not come regularly during the 
season or from season to season, irrigation ensures steady 
yields. Only over a small part of the earth's surface is the 
rainfall large enough or regular enough to insure the high- 
est or steady yields. The so-called humid regions are 
often subject to droughts, and the soils of such sections are 
usually unresistant to drought. The great centers of 
population, with their splendid markets, usually located 
in humid sections, make it especially desirable that large 
and steady yields be obtained by the neighboring farmers, 
particularly the truck-gardeners. For these reasons, 
irrigation promises to become a large practice under humid 
conditions. 

Irrigation in humid climates is not new. Much of the 
European irrigation is done under a relatively high rain- 
fall. Water meadows have been known for centuries in 
England, and many have existed for a half-century or 
more in New England. The practice of irrigation under 
humid conditions has only recently, however, been con- 
sidered seriously and extensively. 

(406) 



IRRIGATION IN HUMID CLIMATES 



407 



242. Dry seasons. — It is an elementary fact of weather 
science that neither the total annual rainfall nor its dis- 
tribution is exactly the same from year to year. The 
average of many years does not, perhaps, vary greatly, 
but from year to year there is a considerable difference. 
This constitutes the main reason for irrigation in humid 
districts. For instance, Williams has compiled the follow- 
ing table from the United States Weather Bureau, covering 
ten years, from 1899 to 1909, showing the average annual 
rainfall, the nmnber of droughts or periods of fifteen days 
with less than 1 inch of rainfall, for five points in the 
United States, representing five great divisions of the 
country. In the first column is shown the point at which 
the observation was made; in the second column, the 
average annual rainfall in inches; in the third column, the 
number of fifteen-day periods or over with less than 1 inch 
of rain, or periods of drought; in the fourth column, the 
number of days when irrigation was required, meaning 
the number of days beyond the fifteen days during which 
less than 1 inch rainfall was received. 



Stations 


Average 
annual 
rainfall 


Number of 15-day 

periods or over 

with less than 

1 inch of rain 


Number of days 

when irrigation 

was required 


Ames, Iowa .... 
Oshkosh, Wis. . . . 

Columbia, S. C. . . . 


30.39 
29.78 

47.47 
47.55 
50.75 


23 
27 
46 
62 

60 


190 
292 
352 
568 
724 



It may be noted in the above table that at Ames, 
Iowa, with an average rainfall of over 30 inches, there were, 
in ten years, twenty-three periods of drought, with 190 
days when irrigation would have been beneficial. At 



408 



IRRIGATION PRACTICE 



Oshkosh, Wisconsin, with a rainfall of practically 30 
inches per year, there were twenty-seven such, periods of 
drought, sixteen of which came in the spring and early 
summer, and one of which lasted fifty-nine days. At 
Vineland, New Jersey, with a rainfall of 47 inches, there 
were forty-six such droughts, and 362 days during which 
irrigation would have been helpful. At Columbia, South 




Fig. 118. The annual rainfall of Milan (famous for its irrigation), compared with 
that of humid and arid districts in the United States. 

Carolina, of the sixty-two droughts occurring in the ten 
years, twenty-seven lasted from twenty to thirty days, 
four from forty to fifty days, and one lasted sixty-one 
days, showing the frequent occurrence of rather long 
droughts in that section of the country. At Selma, Ala- 
bama, with over 50 inches of rainfall, sixty periods of 
drought occurred, with 724 days needing irrigation. 

The facts of this table are only representative of a vast 
mass of information of a similar character gathered by the 



IRRIGATION IN HUMID CLIMATES 



409 



Weather Bureau. No part of the country, no matter 
what its total annual rainfall may be, is wholly free from 
periods of drought. Occasionally, these periods are so long 
and so severe as to cause almost the absolute failure of 
crops with all the evils attending crop failure. It is to 
protect the farmer against such periods of drought that 
irrigation in humid regions is advisable. 

243. Results of irrigation in humid regions. — Irrigation 
in humid regions, as already suggested, is not a new prac- 
tice; it has simply 

Irrigated 



Platl 



Not Irrigated 

V///////////X 



Irrigated 



Not Irrigated 

V//////////X 



Fig. 119. Comparative yields of strawberries, 
irrigated and unirrigated. (Connecticut, 
1895J 



failed to arouse any 
large interest among 
the people living under 
humid conditions. In 
recent years, consider- 
able experimental 
work has been con- 
ducted in various 
parts of the humid 
regions of the United 
States, having in view 
the determination of 
the advantage resulting from the use of irrigation water 
in localities that may safely be classed as humid. 

Bowie investigated about 125 irrigated meadows, in 
four counties, in the state of Pennsylvania, the average 
yields of which were contrasted with similar unirrigated 
meadows in the same localities. The average of the 125 
observations showed that irrigation just doubled the yield. 
In other states, similar investigations of meadows have 
been made, with practically the same results. In the 
eastern United States, irrigation doubles the harvests 
from ordinary meadows. 



410 IRRIGATION PRACTICE 

Waters conducted experiments under Missouri con- 
ditions, and, while the work was not continued long 
enough to give averages for a variety of climatic con- 
ditions, it was found that a great increase in the yield 
resulted from the application of irrigation water. As- 
paragus, grown without irrigation, was thin and covered 
with rust; when irrigated it was plump and free from rust. 
Yield and quality were increased by irrigation. Onions 
and corn both yielded larger crops under irrigation. 

Crane, working under South Dakota conditions, found 
that every crop he investigated yielded twice as much 
when irrigation water was applied. His studies were 
almost entirely with artesian water, and the increase in 
crop-yields proved abundantly that whenever such waters 
can be obtained they may be used with great profit. 

Voorhees carried on extensive investigations, chiefly 
during the years 1898 and 1899, to discover if the use of 
irrigation water influenced materially the yield of crops in 
New Jersey. He found, as expected, that the season is the 
important factor in determining the value of irrigation. 
If the growing season was an abundantly wet one, irrigation 
had less effect than when the season was relatively dry. 
The averages of the results obtained by Voorhees for the 
two years in question are exceedingly instructive. 

Blackberries, several varieties of which were tried, 
showed an increase, due to irrigation, of nearly 77 per 
cent of the yield without irrigation. Raspberries, repre- 
sented by several varieties, increased over 37 per cent, 
varying from 70 per cent to a loss when the natural pre- 
cipitation was high. Currants, represented by a number 
of varieties, increased over 28 per cent, varying from 91 
to a loss. Gooseberries, represented by a number of va- 
rieties, increased 3.3 per cent, varying from 109 per cent 



IRRIGATION IN HUMID CLIMATES 411 

to a loss. That is, every experiment undertaken by 
Voorhees yielded average large returns, for small fruits, 
by the application of irrigation water. Phelps, working 
in Connecticut, in 1895, obtained similar results. Straw- 
berries grown under irrigation in Connecticut yielded a 
harvest 159 per cent greater than that obtained without 
irrigation. 

King conducted a long series of similar experiments 
under Wisconsin conditions, and his results confirm, in 
every particular, the conclusions of other investigators. 
King found that irrigation increased the yield of potatoes 
46 per cent; cabbage, 12 per cent; corn, 55 per cent; and 
clover, barley, strawberries, and many other crops under 
experimentation showed large increases under irrigation. 
Maxwell studied, for a number of years, sugar-cane irri- 
gation in the Hawaiian Islands, under an annual pre- 
cipitation of about 47 inches. During the year 1897-98 the 
yield of sugar was increased nearly 1,500 per cent by irri- 
gation. 

It may be that these large increases from irrigation 
are partly due to the fact that under irrigation much 
closer planting is allowed without drying out the soil. 
However that may be, the increase is really due to the 
fact that there is no shortage of water during the growing 
period. It has been amply demonstrated that the arti- 
ficial application of water on humid lands does increase 
•the harvests. Whether the increase and certainty of 
crop-yield will pay for the cost of building the irrigation 
system and of applying the water must be worked out by 
each farmer in accordance with the conditions that sur- 
round him. Field crops which yield a small acre return 
may not pay for irrigation, but truck crops, yielding large 
acre returns, will often pay in one season for the instal- 



412 



IRRIGATION PRACTICE 



lation of the irrigation plant and leave a margin besides. 
Irrigation in humid climates probably always pays, unless 
exceptional difficulties are encountered in securing and 
distributing water. One drought, unprovided against, 
frequently causes a loss that would pay for the irrigation 
system and much else. 

244. Methods of applying water. — The methods of 
applying water in humid regions are those in general use 




Reservoir -^v. />,. 



Ufc 



e *. 



5N 



v J>o 



Public Road 




Pumping 

Station) 



Fig. 120. An irrigation plant in Pennsylvania 



everywhere. Furrowing is probably best, except where 
the soil is very clayey, or where meadows are flooded with 
water. In humid regions, on many relatively small tracts 
devoted to irrigation, specialized crops are usually grown, 
yielding high acre returns. Under such conditions it is 
often feasible to install special irrigation devices, such as 
sprinkling from permanently fixed pipes or from the nozzles 
of movable hose. Such methods are wasteful of invest- 
ment, labor and water and are practically out of the ques- 
tion for large areas. Sub-irrigation also is advocated under 
humid conditions, but the arguments already urged against 
sub-irrigation, unless natural, hold under humid condi- 



IRRIGATION IN HUMID CLIMATES 413 

tions. There should be no differentiation in the irrigation 
practices of humid and arid regions. In both regions there 
should be an adaptation of the general principles to the 
special needs of the community. 

245. The duty of water. — Since irrigation is merely 
supplementary to the rainfall, less irrigation water is ordi- 
narily required in humid regions than in arid regions. 
One to 3 inches of water applied at each irrigation is 
common under humid conditions, and is apparently 
abundant. In arid regions, on the other hand, 3 to 5 
inches, or even more, are applied at each irrigation. In 
the humid regions, plants are likely to be somewhat 
shallow-rooted, owing to the abundance of moisture in the 
early growing season. This makes it unnecessary for the 
roots to move deeply in the soil and therefore more 
frequent irrigation is probably necessary than in arid 
regions. However, the application of water every ten or 
fifteen days should be sufficient. In general, the duty of 
water in humid regions should be higher than in arid 
regions, but this does not always follow, for it is reported 
that to irrigate sugar cane, under humid conditions, a 
depth of water equivalent to 40 to 100 inches is used 
throughout the season, which is much more than is neces- 
sary in the arid regions. It is probable that, in humid as 
in arid regions, the tendency will be to use too much 
water. Over-irrigation is just as objectionable in humid 
as in arid climates, and for the reasons already stated 
in previous chapters. 

246. Sources of water. — The humid region abounds 
in creeks, ponds, rivers and underground water, all of 
which are suitable for irrigation. However, water-rights 
in the East, where irrigation has received little attention, 
are more complicated, and frequently it is more difficult 



414 IRRIGATION PRACTICE 

there than in the West to claim water for agricultural 
purposes. Consequently irrigation in the humid regions, 
at least in the beginning, must be more of individual 
effort and less of community action. Independent, small 
plants must be established, which, in time, may lead to 
cooperation. Meanwhile, many natural waters may be 
impounded; springs may be enlarged, water may be lifted 
by the stream current from the rivers, windmills and other 
engines may be made to lift water from wells, and artesian 
waters may be developed. Since underground water is 
more available under humid conditions than under arid 
conditions, the pumping plant may become a chief de- 
pendence on the irrigated farms of the East. Such pump- 
ing plants need be in operation only at the very time that 
water is needed for the farms. 

247. Water-conservation methods. — In the humid 
regions, the farmer has depended on the rainfall and has 
given little attention to cultural methods for conserving 
water. Beyond question, humid agriculture would be 
greatly improved if the farmers should adopt the simple 
methods of dry-farming for storing and retaining the 
water that falls upon the soil, by proper plowing, surface 
tillage and other methods. This, alone, would eliminate 
many of the droughts that trouble the humid regions. 
Irrigation, then, would need to be called less frequently 
into service. Before the droughts of the world shall 
finally cease to vex man, it is necessary for both dry- 
farming and irrigation methods to be adopted in the 
humid regions of the world. 

248. Value of sewage water. — Sewage irrigation, while 
not necessarily practised under a high rainfall, is closely 
associated with irrigation in humid regions for the reason 
that most of the larger cities, boasting the largest quan- 



IRRIGATION IN HUMID CLIMATES 415 

tity of sewage, are, as yet, located under a considerable 
rainfall. The materials dissolved or suspended in irrigation 
water are often, as shown in Chapter V, of high value as 
plant-food. Of all known waters, however, sewage water 
is usually of the highest value in crop-growth, since its 
chief constituent, human waste, approaches in composition 
the more valuable portions of plants. 

It has been roughly calculated that each person, living 
in a city, wastes annually eight pounds of nitrogen, three 
pounds of potassium, two pounds of phosphorus, not 
counting the organic matter of which these three funda- 
mentally important elements are parts. When these 
quantities are multiplied by the millions residing in many 
of the large cities, the sewage which passes into the rivers 
and oceans, rises to tremendous value. The large cities 
cause the largest single losses, but the smaller cities of the 
country are now installing sewage systems, and all should 
give some attention to the conservation of sewage waste. 
Sewage can best be put to use by its application in irri- 
gation. 

249. The use of sewage. — In many countries, sewage 
water is used for plant-production. The most famous 
example is that of Craigentinny meadows, receiving sewage 
from Edinburgh. According to Storer and King, one 
hundred years ago, when sewage irrigation began on these 
fields, they were originally a waste. With the aid of sewage 
irrigation they have produced continuously since that time 
large crops of grass, with a profit far above that of the 
best fields of the country. Similarly, near Milan in Italy, 
sewage is let into great canals that lead to great meadows. 
These have produced remarkably, as a result of the appli- 
cation of the heavily fertilized water. China, and the 
Orient generally, are perhaps the greatest examples of the 



416 IRRIGATION PRACTICE 

wise use of human waste in crop-production. In these 
countries, modern sewage systems have not been installed, 
but the human waste is carried in specially provided re- 
ceptacles to the farms. It is not likely that this method 
will be adopted under civilized conditions; human waste 
will continue to be thrown into sewage systems, but, as 
among the Chinese and other nations that have estab- 
lished a permanent system of agriculture, the sewage 




Fig. 121. Distribution of water on Craigentinny Meadows, Edinburgh. 

water thus produced must be used for the production of 
crops. 

It has been argued that, for health reasons, sewage 
should not be so used, for disease germs might be carried 
by sewage water to the herbage and thence to domestic 
animals and finally to human beings. The fact that sewage 
irrigation has been practised for centuries with no evi- 
dence of such evil effects leads to the belief that the 
danger does not exist. Sewage, if properly applied to a 
soil which is properly tilled, is thoroughly oxidized and 
becomes innocuous. Plants, themselves, would not be 



IRRIGATION IN HUMID CLIMATES 417 

likely to take up disease germs. Every open water channel, 
especially in settled sections, contains to some degree the 
substances of ordinary sewage, yet none hesitate to 
use such water for irrigation purposes. The matter could 
well be subjected to experimental inquiry, before extensive 
sewage irrigation is undertaken. 

It is ordinarily quite difficult to make the best use of 
sewage water, because the outlets of sewage systems are 
usually in low places, and the main problem is that of 
lifting water to fields. However, in many places it is pos- 
sible to take out the river water some distance below the 
outlet of the system and there to apply it to fields. In 
other places, the sewage might be run into reservoirs and 
then be pumped to the fields. 

250. Factory and mill waste. — While, in general, sew- 
age waters are admirably adapted to the production of 
vegetable matter, yet it must not be forgotten that 
certain kinds of waste are detrimental to plant growth. 
For instance, the sewage or waste from certain factories 
and mills is injurious. In the West, it has been found fre- 
quently that waters coming from gold and silver mills 
contain poisonous elements. Copper mills have likewise 
been shown to contaminate water to such a degree that 
its irrigation value is greatly reduced. Attention should 
be given, even in the open country, to the possible con- 
tamination of water by substances which are injurious to 
plants and animals. 

REFERENCES 

Bowie, Aug. J., Jr. Irrigation in the North Atlantic States. United 
States Department of Agriculture, Office of Experiment Sta- 
tions, Bulletin No. 167 (1906) 

King, F. H. Irrigation in Humid Climates. United States Depart- 
ment of Agriculture, Farmers' Bulletin No. 46 (1896). 
AA 



418 IRRIGATION PRACTICE 

King, F. H. Farmers of Forty Centuries. Mrs. F. H. King, Madison, 
Wisconsin (1911). 

Maxwell, Walter. Irrigation in Hawaii. United States Depart- 
ment of Agriculture, Office of Experiment Stations, Bulletin 
No. 90 (1900). 

Mead, Elwood. Irrigation Investigations in Humid Sections of 
the United States in 1903. United States Department of Agri- 
culture, Office of Experiment Stations, Bulletin No. 148 (1904). 

Phelps, C. S., and Voorhees, Edward B. Notes on Irrigation in 
Connecticut and New Jersey. United States Department of 
Agriculture, Office of Experiment Stations, Bulletin No. 36 
(1897). 

Voorhees, Edward B. Irrigation in New Jersey. United States 
Department of Agriculture, Office of Experiment Stations, 
Bulletin No. 87 (1900). 

Williams, Milo B. Possibilities and Needs of Supplemental Irri- 
gation in the Humid Regions. United States Department of 
Agriculture, Yearbook for 1911. 

Yoder, P. A. Poison in Water from a Gold and Silver Mill. Utah 
Experiment Station, Bulletin No. 81 (1903). 



CHAPTER XX 
IRRIGATION TOOLS AND DEVICES 

Fakming under irrigation may and does use practically 
every approved farm tool found desirable under humid 
conditions. Every refinement known to agriculture may 
be practised with profit by the farmer under the ditch. 
Plowing at the correct time, to the best depth and by the 
accepted methods, lies at the foundation of successful 
irrigation-farming and humid-farming. To plant correctly; 
to supply the plants with sufficient food; to remove weeds, 
and to harvest wisely — are all practices to be observed as 
carefully by the irrigation-farmer as by the rainfall- 
farmer. 

The special tools and devices for irrigation farming are 
those only that are used directly for the distribution upon 
the land of water from the canal and the conservation of 
it in the soil. 

251. Clearing and breaking the land. — The pioneer 
irrigationist will usually find his new farm unbroken. 
It is either covered by sage-brush or similar plants or in 
the firm sod of the plains. Sod land may be easily broken 
by a breaking plow, many forms of which are found on the 
market. 

Sage-brush land is, however, much more difficult to 
clear. One of the most effective methods is to drag over 
the land two parallel railroad irons which pull up most of 
the sage-brush. The remaining clumps must be grubbed 
out by hand. Sometimes the railroad irons are joined in a 

(419) 



420 



IRRIGATION PRACTICE 



V-shape, and shod on the outside with iron cutting-edges. 
Such an iron "snow-plow' ' is also very effective in clearing 
sage-brush from the land. The most effective method, 
when it can be used, is to burn off the brush. In the inter- 
mountain country with dry summers, the brush often 
becomes very dry in late summer, and on a day when a 
light wind is blowing it may be possible to remove the 
brush from a large area. The obvious dangers that 
accompany fire must always be considered. Many 
machines are on the market for removing sage-brush; 



-"? t. k H_ 1. -- / -* i k \ 

<tm - ~ ----.-..m.v> 



\:4 *' 








Fig. 123. Section of 
V-ahaped flume. 



Fig. 122. Section of cement flume. 




/ Fig. 124. Wooden flume. 



BOTTOM JOINT 
Fig. 125. Section of rectangular flume. 



none are wholly satisfactory, and as the country is taken 
up, there will be no further need for them. 

252. Laying out the farm. — Once the land has been 
cleared, the farm should be laid out with reference to the 
crops to be grown, rotations to be followed, and the most 
effective methods of applying water. The characteristic 
feature of farming under irrigation makes it of first 
importance that the lay-out be made with direct reference 
to the location of the irrigation ditches that must cover 



IRRIGATION TOOLS AND DEVICES 



421 



the farm. This should be done with extreme care, for 
any mistakes made in the placing of irrigation ditches will 
mean loss in time and money when a new system is built. 

In general, water 
should be delivered 
from the supply lateral 
at the highest point 
of the farm. This 
makes it possible to 
distribute water over 
the whole farm. In 
earlier days, all the 
farm ditches were 
carried along ridges 
or high lines of the 
farm. This method 
led to the formation of irregular and somewhat unsightly 
fields, awkward to fit into a system of rotation. While it 
is indispensable that the farm ditches follow, in a general 
way, the contour lines of the farm, yet an irrigated farm 
may be laid off into regular, rectangular fields by the 
use of special devices to carry the water across depres- 
sions of the land. 

The most common method of securing straight ditches 
on the farm is the use of earthen levees, to carry the 




Fig. 126. Flume with lateral gate. 







Fig. 127. Buck scraper. 



422 



IRRIGATION PRACTICE 




Fig. 128. Leveler or float. 



water across the low places. Earthen levees cost little 
and may be made by the farmer, and, although subject 
to frequent washouts during the first two or three years, 
give no further trouble after they are once established. A 
more desirable method, when it can be afforded, is the 
flume or the pipe to carry water across low places. Tri- 
angular and rectangular flumes are used. Wooden flumes 




Fig. 129. Shuart grader. 



IRRIGATION TOOLS AND DEVICES 



423 



give very good satisfaction while they last, but are not 
so permanent as the concrete flumes which are now being 
constructed extensively. Recently, also, galvanized iron 
pipes or concrete pipes are used with success for carrying 
water over the farm. 

The second guiding principle in laying out the ditches 
on the farm should be that they be as inconspicuous as 
possible and out of the way of the regular operations on 
the farm. For that reason the 
ditches are often made to follow 
the fences separating the farm fields, 
and are even buried underground as 
pipes, with openings at proper places 
to supply the smaller laterals. (Figs. 
122-125.) 

253. Leveling the land. — Natural 
land is seldom of even or regular sur- 




Fig. 130. Soil auger. 




Fig. 131. Lateral plow. 



424 



IRRIGATION PRACTICE 




Fig. 132. V-crowder. 

face. Slight elevations and depressions cover it. The 
more even the land is, however, the more easily and 
uniformly may irrigation water be applied. Water 
applied to uneven land accumulates in the lower places 
and over-irrigates the plants there growing, while the 
plants on the higher places receive little or no water. 
Consequently, the yield of the crop is reduced. Moreover, 

such irrigation re- 
quires much labor, 
and is unsightly. As 
soon as the layout 
of the farm has been 
decided upon, steps 
should be taken to 
grade or level the 
land. The work once 
done properly need 
Fig. 133, Building a ditch. not be done again, 




TVPlCflL FORMS 

F~£JRM PITCHEIS 




No.i. 



No.a. 



iso.3. 









NO.4. 




Another form, of No.4. 



K- » 



ha'-t- 



^SSfJ^'V Original *■ v ; • ^:jvr???7;a)^ 



t S^TiS^^! 

T ~~ ^~ _rz^ gkr^ rW ' Surface ^ 




Another form of INO.3. 



Fig. 134. Typical forms of farm ditches. 



426 



IRRIGATION PRACTICE 



and from the first irrigation may be done in the best 
manner. 

Land may be leveled by any of the many machines on 
the market. The regular scrapers or graders may be used 




Fig. 135. Concrete drop in ditch. 

for reducing the high points, and plank-levelers or floats 
may be used for the final grading. (Figs. 127-129.) In 
cutting down the high places, it is well to know something 
of the subsoil. If the top soil is underlaid near the surface 
with a lifeless clay it may not be wise to carry the grading 
too low, or especially, to scatter the clay on the lower- 
lying land. In such cases, slight grading through successive 
years may be more satisfactory. For studying the sub- 
soil, a soil auger is very useful. (Fig. 130.) 

254. Making farm ditches. — After the layout of the 
farm has been decided upon, the main supply ditches 
placed, and the land leveled, the farmer may construct 
the necessary laterals or farm ditches, fed by the larger 
supply ditches. The location of the farm ditches must be 



IRRIGATION TOOLS AND DEVICES 



427 



determined by the layout and contour of the farm. All 
ditches, whether large or small, must follow, in general, 
the ridges of the land. 

Farm ditches may be made by any machine that will 
make a furrow in the ground. The first modern irrigation 
ditch in America was made by an ordinary moldboard 
plow, the furrow from which was cleaned out with shovels. 
Thousands of small farm ditches have been made in that 
way since that first day of irrigation. The lateral plow or 
winged shovel plow is now more frequently used in ditch- 




Fig, 136. Drop in flume. 



428 



IRRIGATION PRACTICE 



making. (Fig. 131.) The adjustable crowder, as shown in 
Fig. 132, is extensively used in removing the loose dirt 




LARGE COLLAR 



Fig. 137. Distributor for hose. 

from the plow furrow. If the ditch is large, the scraper is 
used for that purpose. 

Farm ditches must be constructed with reference to 
the quantity of water 
required by the land 
that they are to serve. 
The quantity of water 
that may be carried 
by a ditch depends 
fully as much upon 
its fall or grade as 
upon its width and depth. The smaller the volume 
carried by a ditch, the greater the grade 
required to secure the same velocity 
of flow. In a small ditch capable 
of carrying about X)4> second- 
feet of water, a fall of 2 
inches to the rod 




Fig. 138. Attaching hose to distributor. 




Fig. 139. Leveling device. 



IRRIGATION TOOLS AND DEVICES 



429 




would produce a velocity of 
2 feet a second, while in a 
ditch capable of carrying about 
24 second-feet, the fall re- 
quired to give the same veloc- 
ity would be only J4 mcn to 
the rod. The nature of the 
soil determines chiefly the 
grade that may be adopted 
for farm ditches. In fine sand 
or silt a mean velocity of 1 



Fig. 140. Lateral headgate. 




Fig. 142. Dammer. 



Fig. 143. Board 
dam. 




Fig. 144. Canvas dam. 

OPENING 6X&' 



Fig. 146. Metal dam. 





Fig. 147. Distribution of water from flume 
to furrows. 



Fig. 145. Canvas dam with opening. 




Fig. 148. Distribution through wooden tubes 






(430) 



IRRIGATION TOOLS AND DEVICES 



431 



foot per second is often the maximum, while m clay, a 
velocity of 3 feet per second may be adopted. Some soils 
"wash" so easily that a very small velocity only may be 
used. The farmer 
must learn for himself 
the nature of his soil 
and the ditch grades 
that may be safely 
adopted. In ordinary 
materials a velocity 
of 2 to 2Y 2 feet a 
second are considered 
safe. Naturally the 
grade of the ditch can not exceed that of the land. 
Fortier has figured the flow of water in each of five 
types of farm ditches (Fig. 134) which cover ordinary 
farm conditions. His results follow. 




Fig. 149. Lath check. 



zdto zS-\ 0ojm 1 2 or ye"/?'*"* 



Qtnerf/oir stond 




OVEXFLOV* SYSTEM 



'or i6 'Basin W>M vb'"* 




"S "Cerneof 



Pressure System. 

Fig. 150. Conducting water down inclines in concrete pipes. 



432 



IRRIGATION PRACTICE 



Mean Velocity and Discharge of Ditches with Different 

Grades 

Farm Ditch No. 1 



Grade 


Mean velocity 

in feet per 

second 


Discharge in 


Inches 
per rod 


Feet per 
100 feet 


Feet per 
mile 


cubic feet 
per second 


V2 


.25 


13.33 


1.01 


.67 


% 


.38 


20.00 


1.23 


.81 


1 


.51 


26.67 


1.42 


.93 


IX 


.63 


33.33 


1.59 


1.05 


iy 2 


.76 


40.00 


1.75 


1.16 


2 


1.01 


53.33 


2.04 


1.35 


2V 2 


1.26 


66.67 


2.28 


1.50 


3 


1.51 


80.00 


2.50 


1.64 


sy 2 


1.77 


93.33 


2.70 


1.78 




Fig, 151. Roller furrower. 



IRRIGATION TOOLS AND DEVICES 



433 



Mean Velocity and Discharge of Ditches with Different 

Grades, Continued 

Farm Ditch No. 2 



Grade 


Mean velocity 

in feet per 

second 


Discharge in 


Inches 
per rod 


Foot per 
100 feet 


Feet per 
mile 


cubic feet 
per second 


K 


.13 


6.67 


.82 


80 


l A 


.25 


13.33 


1.16 


1.00 


% 


.38 


20.00 


1.42 


1.30 


l 


.51 


26.67 


1.64 


1.50 


IK 


.63 


33.33 


1.84 


1.70 


iy* 


.76 


40.00 


2.02 


1.80 


m 


.88 


46.67 


2.18 


2.00 


2 


1.01 


53.33 


2.34 


2.10 


2V 2 


1.26 


66.67 


2.61 


2.40 







Farm Ditch No. 


3 




Vs 


.06 




3.33 


.79 


2.08 


K 


.13 




6.67 


1.13 


3.00 


V2 


.25 




13.33 


1.60 


4.20 


% 


.38 




20.00 


1.97 


5.20 


l 


.51 




26.67 


2.28 


6.00 


IK 


.63 




33.33 


2.57 


6.80 





Farm Ditch No 


4 




i 

16 


.03 


1.58 


.84 


4.20 


Vs 


.06 


3.33 


1.08 


5.40 


K 


.13 


6.67 


1.54 


7.70 


Vs 


.19 


10.00 


1.89 


9.50 


V* 


.25 


13.33 


2.20 


11.00 


% 


.31 


16.67 


2.45 


12.20 


% 


.38 


20.00 


2 69 


13.40 



When the natural grade of the land is so steep as to 
make it dangerous to employ ditches of the same grade, 
suitable drops must be installed at various points. (Figs. 
135, 136.) To carry water from the laterals to furrows, in 



434 



IRRIGATION PRACTICE 




Fig. 152. Utah lay-off and pulverizer. 

soils that "wash" easily, lath boxes, already mentioned, 
or pipes are often used. (Fig. 137, 138.) 

In constructing ditches it is usually sufficient to step 
off the distances, and any simple leveling device gives the 
necessary levels. (Fig. 139.) 

255. Gates and checks. — Gates for the admission of 
water from the supply ditches into the laterals may be 




FlQ. 153. Robinson's adjustable corrugator and renovator. 



IRRIGATION TOOLS AND DEVICES 



435 




Fig. 154. Ridger in check and basin irriga ion. 



made in almost any 
way to suit the farmer, 
from a simple board, 
removed when the 
flow is desired, to 
elaborate doors 
hoisted by machinery. 
In ordinary farm 
practice, permanent 
plain wooden or con- 
crete frames into 
which the gate may 
be dropped constitute 
the most effective 

rlpvifp fTTifr 14-0 ^ ^ IG * *^' Rigger in check and basin irrigation. 

To guide the water from the lateral ditches on to the 
land, devices to check or dam the flow are employed. The 





Fig. 156. Furrower in action. 




Fig. 157. Cultivator. 




Fig. 158. Cultivator attachments. 
(436) 



IRRIGATION TOOLS AND DEVICES 



437 



most common check is a shovelful of dirt placed in the 
ditch at the point where the division of water is desired. 
At times the checks are made by a dammer, while the 
ditch is dry before the irrigation. The dirt check is only 
temporary, is often washed away, and involves consider- 
able labor. A portable wooden dam or check, or dam 
made of a board with one or more holes in it, which can 





Fig. 159. Beet cultivator attachments. 

be inserted wherever needed and removed at will, has 
been found very satisfactory. The metal dam or tappoon 
has also given satisfaction. The canvas dam has of recent 
years been extensively adopted, and is said to be of 
especial value because it may be made to fit the ditch 
snugly. It is held down by a shovelful of dirt, so that it 
is really a modification of the original dirt check. The 



438 



IRRIGATION PRACTICE 




Fig. 160. Cutaway disk harrow. 

canvas dam is made of a piece of strong canvas, nailed 
firmly to a wooden cross piece. At times there is an open- 
ing in it to divide the irrigation stream. Sometimes a 
small obstruction such as a submerged flashboard or a 
lath dropped across the bottom of the ditch is sufficient 
to divert the water into the lateral. (Figs. 141-150.) 

I 




Fig, 161. Clod crusher, pulverizer, leveler and smoother. 



IRRIGATION TOOLS AND DEVICES 



439 




Fig. 162. Frieze water register. 

256. Ridging and furrowing. — The 

field-ditch method of irrigation requires 
only that a few rather small furrows 
may be made to assist in guiding the 
water over the land. These furrows are 
ordinarily made by the point of the 
hoe or as a very shallow plow furrow. 
The check, border and basin methods 
of irrigation require that ridges or 
levees be thrown up around the plots. 
For this purpose any of the ordinary 
farm implements may be employed, 
although special "ridgers" and "crowd- 
ers" are made and used on many 
farms. 

The furrow system of irrigation 
requires that parallel, uniform furrows 
be made for guiding the water over the 
land. These may be made by hand with a hoe, but only 
with great labor. Numerous devices have been proposed 
for making uniform furrows with horse labor. The shovel 
attachment to the cultivator has been used, but with 




440 



IRRIGATION PRACTICE 



'•'"■•.. 



indifferent success, because the furrows were not left 
smooth. One of the first devices of the Utah pioneers 
was a large roller with several wooden "shoes" each one 

of which made a fur- 
row. (Fig. 151.) This 
gave excellent satis- 
faction except that 
the rolling of the land 
made rapid evapora- 
tion possible. From 
this implement has 
developed the Utah 
layoff and pulverizer 
(Fig. 152), especially 
adapted for alfalfa fields. The furrows are cut, the clods 
pulverized and the smoothed ground mulched by a rear 
attachment of spike teeth. Many other devices for fur- 
rowing have been made. (Figs. 153-156.) 

257. Mulching the soil. — Well-cultivated soils produce 
crops with the least expenditure of water. Implements for 
cultivation are therefore of the highest importance to the 
farmer. Such implements are now on the market in great 







Fig. 163. Device for measuring miner's inches. 




Fig. 164. Cross section of canal for measurement of flow. 

numbers. Clods may be broken by the corrugated roller; 
the alfalfa fields disked by the disk with jagged cutting 
edges; the mulch may be made by one of the tooth harrows, 
the disk-harrow or any one of the many available culti- 



IRRIGATION TOOLS AND DEVICES 



441 



vators. The main thing is to fit the tool to the crop and 
the soil. Particularly important is the soil. Most harrows 
and cultivators are now so built that different kinds of 
teeth and shovels may be attached; thereby a much larger 
field of service is possible. (Figs. 157-161.) 

258. Measuring the flow of water. — Brief consider- 
ation of this subject has been given in Chapter XVII. 




Fig. 165. Current meters. 



Special engineering treatises should be consulted for more 
information. All in all, some form of the weir is the best 
measuring device on the farm. It often becomes desirable 
for the farmer to keep a constant record of the water 
flowing over a weir. To do this, automatic registers con- 
nected with floats, and run by clockwork, have been 
devised. The rising and falling of the float, indicating the 



442 



IRRIGATION PRACTICE 



rise and fall of the water, is registered on a record sheet 
that may be preserved for future use. (Fig. 162.) 

Where miners' inches are units of measurement, de- 
vices like that of Fig. 163 are used. The United States 
Geological Survey makes a cross-section of a canal or 
river at a given point (Fig. 164) and determines the velocity 
of the flow there, with current meters. (Fig. 165.) Many 




special measuring devices are also available, as the Grant- 
Mitchell meter. (Fig. 166.) 

Similarly, a great number of water divisors, in addition 
to those mentioned in Chapter XVII, have been tried 
out with varying success. 

A very great amount of work has been done by engi- 
neers on the measurement of flowing water. The results 
obtained are of high practical value. It must be said, 
however, that the engineers, themselves, have not as yet 
agreed upon the measuring device best suited to the use 
of the farmer. Engineering books should be consulted 
for further information on this subject. 



444 IRRIGATION PRACTICE 

REFERENCES 

Fortier, Samuel. Practical Information for Beginners in Irriga- 
tion United States Department of Agriculture, Farmers' 
Bulletin No. 263 (1906). 

Johnston, C. T., and Stannard, J. D. How to Build Small Irri- 
gation Ditches. United States Department of Agriculture, 
Farmers' Bulletin No. 158 (1902). 

Teele, R. P. Preparing Land for Irrigation. United States Depart- 
ment of Agriculture, Yearbook for 1903. 

Widtsoe, J. A. Dry-Farming. Chapter XV. The Macmillan Com- 
pany (1911). 






CHAPTER XXI 
THE HISTORY OF IRRIGATION 

The history of irrigation is full of interest, for it is 
virtually the story of the most progressive peoples of 
historical times. Like all human history, it is fragmentary 
and can be pieced together only by much labor. The 
history of irrigation is yet to be written; this chapter is 
but a brief and incomplete sketch of the subject. 

259. The antiquity of irrigation. — The practice of 
irrigation antedates recorded history in every great coun- 
try of antiquity. Whether it originated in Asia, Africa, 
Europe or America, no man can tell. Beyond question, 
where man first appeared, there, not long after, irrigation 
began to be practised. Together with the stirring of the 
soil and the sowing of seed, irrigation is one of the first 
agricultural practices of mankind. 

The monuments of Egypt declare that Menes, the 
first king of the first dynasty, extended greatly the irri- 
gation structures of his day. How long before him, in the 
unrecorded past, irrigation had been practised in Egypt, 
is not known. Certain it is, however, that in the succession 
of dynasties, throughout the glory of Egypt, even to the 
present humble day, the waters of the Nile, used in irri- 
gation, have made of Egypt a granary of food. In the 
days of Joseph, the son of Jacob, "all countries" came to 
Egypt for food. 

The monuments of Babylon and Assyria declare with 
equal emphasis that irrigation was a full-grown practice 

(445) 



446 IRRIGATION PRACTICE 

on the vast Mesopotamian plains, when the first records 
were laid aside for our use in the latest day. Hammurabi, 
a contemporary of Abraham, built a great and wonderful 
canal by which the desert was made into gardens, and an 
elaborate system of irrigation covered the Babylonian 
plain, under which grain returned 300-fold. These mighty 
structures fell into disuse and decay as the power of the 




Fig. 168. Sagebrush land. 

ruling nation receded from Babylon, but the remains of 
the canals are visible today, and the fertile soil is as ready 
as ever to respond to the touch of water. Moreover, the 
recently unearthed codes of laws concerning the use of 
irrigation water prove a degree of irrigation refinement 
scarcely ever surpassed. 

In Persia, India, Ceylon, China, Syria, Palestine, and 
practically every country of high antiquity, irrigation has 
been practised, without cessation, since the beginnings of 



THE HISTORY OF IRRIGATION 



447 



history. It is unquestioned that in Egypt and the Asiatic 
countries the practice of irrigation goes back 2,000 years, 
and it may be 4,000 years. 

On the American continent, also, the practice of irri- 
gation goes back to immemorial times. At the time of 
the Spanish Conquest, irrigation practice was found well 
developed, and irrigation structures existed then which 
dated back to the first traditions of the native population. 
In Peru are remains of irrigation structures of undoubted 
antiquity and of a quality comparable with the best of 




Fig. 169. The Doon 



the present day. In Chile, similar remains are found. In 
Argentina, there are remains of vast irrigation structures. 
In fact, along the Atlantic and Pacific drainages of South 
America, wherever the climate made it desirable, great 
irrigation structures were built in a remote antiquity. 
In some places stupendous irrigation canals may be 
traced — 400 to 500 miles long — far beyond our modern 
attempts. There is evidence to show, also, that on the 
American continent refinements of irrigation were prac- 
tised, superior to any others known. 



448 



IRRIGATION PRACTICE 

4 




Fig. 170. Shadof of Egypt or paecottah of India. 

Likewise, in Mexico and the southwestern United 
States are remains of prehistoric canals, which prove 
amply the high antiquity of irrigation in North America. 
To the past belongs the credit of having originated irri- 
gation; our present day must refine it and make it im*- 
perishable. 



THE HISTORY OF IRRIGATION 449 

260. The Christian era, to 1800. — Clearly, a valuable 
practice so ancient and so widespread, as is irrigation, 
could not vanish from the earth. Therefore, in spite of 
the changing fortunes of the race which has covered but 
a small part of the earth, irrigation has remained a con- 
tinuous practice. In some places, as in Babylon, with the 
decline in civilization and the diminution of population, 
irrigation disappeared wholly or in part; while in other 
places, as in Egypt, China and Persia, it has continued 
and often increased. New countries have adopted it; and 
most of the older ones have maintained it. The most 
enlightened peoples have always practised and do now 
practice irrigation, if the climatic conditions make it 
desirable. It is difficult for an unintelligent or shiftless 
people to become good irrigators. 

During the Christian era, the practice of irrigation 
has moved westward, with the general western movement 
of civilization. During the days of the Roman Empire, 
irrigation was fostered in all the Mediterranean countries, 
although relatively few remains of the Roman structures 
are known. That it was of high importance in Roman 
days is well shown by the attention given irrigation in 
the famous codes of law formulated in the fifth and sixth 
centuries after Christ. As another trifling but interesting 
evidence, Carpenter gives the word "rivals," derived from 
"rivus," an artificial water channel, or ditch. The users 
from a "rivus" were rivals — the usual contests over water 
are clearly implied. 

The invasion of southern Europe by the Moors, in the 
ninth and tenth centuries after Christ, became a great 
stimulus to irrigation. The Moorish conquerors had a 
good traditional and practical knowledge of irrigation, 
and sensed quickly the value, to southern Europe, of more 
cc 



450 IRRIGATION PRACTICE 

extensive irrigation. Therefore, during their rule, especially 
in Spain, many large canals were built, and irrigation 
practices perfected. To Roman and Moorish rule, together, 
must be ascribed the beginnings of many of the splendid 
irrigation structures of France, Spain and Italy. 

In France, irrigation has been practised under a great 
variety of conditions. The first great canal in France, 
the St. Julien, seems to date from about 1171. Other and 
minor structures were built in the centuries that followed, 
up to 1800 A. D. 

Spain, among the countries of southern Europe, has 
most need of irrigation, and many of her smaller irrigation 
canals date back to Roman times. After the Moorish 
occupation, from the eleventh to the thirteenth centuries, 
particularly in the valley of the Genii, in Granada, many 
great canals were built, which have endured to the present 
time. The delivery of water was so greatly perfected in 
those days that the Valencia Canal, for instance, has been 
managed for 600 years with the laws that now prevail. 
From the thirteenth century, onward, there was some 
added irrigation development under many of the enlight- 
ened rulers of Spain. The modern irrigation activity 
began in Spain as early as 1759, earlier than in any other 
land. 

Italian irrigation has grown so steadily and intelli- 
gently from the eleventh to the nineteenth centuries that 
Italy has been denominated the classic land of irrigation. 
In the eleventh century, the old Roman canals in Lom- 
bardy were reconstructed. In Italy, the twelfth century 
was marked by tremendous irrigation activity. The 
thirteenth, fourteenth, fifteenth and sixteenth centuries 
all contributed largely to irrigation development, and the 
canals then built are now in service. In the seventeenth 



THE HISTORY OF IRRIGATION 451 

century, under the domination of Spain, the proper details 
of irrigation practice were vigorously promoted and some 
canals were built. During the eighteenth century, few 
large additions were made to the irrigation system of 
Italy, but the existing canals were used diligently. 

After the discovery of America, the zealous Catholic 
missionaries established missions in various parts of the 
two American continents. These priests were chiefly from 
southern Europe and well acquainted with irrigation. 
Whenever a mission was established in an arid section, a 
small irrigation system was also built for the support of 
the mission. The remains of these mission irrigation 
systems are found in various parts of America, notably 
in California. In a few cases, also, the Catholic fathers 
taught the natives irrigation, or rather insisted upon the 
use of the ancient knowledge. The Catholic missionaries 
did not succeed in establishing American irrigation on a 
community scale, beyond that already existing among the 
aborigines. 

During the first 1,800 years of the Christian era, the 
irrigated countries of antiquity continued their irrigation 
practices; the countries of Europe, particularly France, 
Spain and Italy, adopted and extended the practice greatly, 
and the new lands brought under the domination of civi- 
lized man made little or no irrigation progress. 

261. Irrigation in recent times. — The new light of 
advancing science finally showed the great nations of 
the nineteenth century that irrigation is a great world 
problem. Even in the countries of southern Europe, in 
which irrigation had developed under the influence of a 
growing civilization, new structures were planned and 
completed, methods of practice perfected and more intelli- 
gent laws enacted. In France, since about 1839, many 



452 IRRIGATION PRACTICE 

large canals have been constructed; in Spain, also, much 
irrigation progress has taken place during the nineteenth 
century, and in Italy the Great Cavour Canal was built 
about 1844, with minor ones since that date, and in 1865 
the valuable irrigation code of Victor Emmanuel was 
promulgated. 

The greatest recent progress in irrigation has occurred, 
chiefly, under Anglo-Saxon direction in newly settled 
countries or in older settled countries brought under 
Anglo-Saxon rule. 

Thus, in Egypt, under English rule, with the wise 
initiative of Mehemet Ali Pasha in 1820, an irrigation 
revival has begun which promises to eclipse in its results 
the noonday of ancient Egyptian irrigation. The old 
channels have been deepened and extended, new and more 
economical methods of irrigation have been adopted, new 
and profitable crops have been introduced, and, as the 
climax, the great Assuan Dam has been built as the first 
main step toward utilizing the varying flow of the Nile 
in an unvarying manner. True, while this revival began 
early in the nineteenth century, it was only in the last 
quarter of the century that the really big things in recent 
Egyptian irrigation have been done. 

India, under English rule, is likewise in an irrigation 
development far beyond the greatest in the history of this 
age-old land. From immemorial times droughts, with 
consequently fearful famines, have vexed India. Early in 
the nineteenth century, the rulers began to look to an 
extended irrigation for relief from famine. The year 
1878, at the end of a disastrous famine, may be said to be 
the beginning of modern irrigation in India. Commissions 
were appointed, new canals constructed and great efforts 
made to establish a large and thoroughly modern irrigation 



THE HISTORY OF IRRIGATION 453 

system. As a result of these activities, the irrigated area 
of India was increased, between 1877 and 1897, from 6 
per cent to 7.5 per cent of all the arable land. Irrigation 
development in some phase is being pushed with un- 
diminished vigor. 

South Africa has also shared in the recent irrigation 
development. Cape Colony, ceded to England in 1814, 
began its recent growth with the diamond discoveries of 
1870. Soon afterwards, in 1877, irrigation boards were 
organized to consider the small and scattered irrigation 
efforts of the past and to propose new and greater plans 
which have been in part carried out. Since 1904, in the 
other states of British South Africa, irrigation develop- 
ment has been undertaken on a large scale. In fact, so 
urgent had the interest in irrigation become that, in 
1909, an irrigation congress was held for all British South 
Africa. Much irrigation progress may be looked for in 
South Africa. 

Australian irrigation has had a similar history. Iso- 
lated irrigation plants were established soon after the 
settlement of the continent, but it was only in 1884 that 
a royal commission was appointed to consider ways and 
means of irrigation development. Since 1885 govern- 
mental consideration has been given to irrigation with the 
result that notable structures have been built and much 
advance made in the reclamation of the arid lands. 

In many other countries, on all the continents, interest 
in irrigation has been developed in recent years, and in 
many of them irrigation dams and canals have been 
constructed. Argentina, for example, although only at the 
threshold of her agricultural development, has already 
constructed several irrigation works of considerable 
extent. 



454 IRRIGATION PRACTICE 

The greatest recent progress in irrigation has come 
about in every country during the last forty or fifty years. 
The year 1880 may well be taken as a convenient marker 
for the beginning of modern irrigation on a large scale, 
with governmental support and based upon modern 
knowledge. 

262. The founding of modern irrigation in America. — 
During the first half of the nineteenth century, there was 
no irrigation progress in America. The native Indians 
in some few places in Mexico and South America, were 
irrigating small fields. The old missions in the United 
States were falling into decay. The European conquerors 
of the new continent were busily engaged in the humid 
portions of the country. The more arid or remoter parts 
of the country had been explored only by the handful of 
trappers and a few others, who had ventured westward 
largely in search of adventure or scientific truth. The 
great territory now covered by the mountain states was 
designated on the school maps as the Great American 
Desert, and with the country adjoining it on every side, 
was held to be unfit for agricultural purposes. 

The opening of the Oregon country brought venture- 
some settlers across the continent more frequently, until 
the old Oregon trail was pretty well defined, but those 
who traveled it sought their homes on the Pacific Coast, 
where the rainfall was quite as heavy as in the far East. 
The old southwest trail from Santa Fe was practically 
unused by emigrants. There was no American irrigation 
of any consequence during the first half of the nineteenth 
century. 

Early in the spring of 1847, a party of pioneers, under 
the leadership of Brigham Young, set out from their 
winter camp, near what is now Council Bluffs, to find in 



THE HISTORY OF IRRIGATION 



455 



the far West a place where their people could settle. On 
July 24, 1847, this party of pioneers entered the Great 
Salt Lake Valley, chosen as the place of settlement, and 
on that day planted potatoes in what is now the business 
section of Salt Lake City, and gave the soil a "good 
soaking" of water brought from the neighboring City 
Creek through a plow furrow that served as a ditch. 
This was the birth of modern irrigation in America. 




Fig. 171. Caravan crossing the plains in early irrigation days. 

The Mormon pioneers possess the honor of having 
founded modern irrigation in America, not because of the 
initial irrigation on July 24, 1847, but because the Mormon 
people continued the work, dug extensive canals, brought 
thousands of acres under irrigation, devised methods of 
irrigation, established laws, rules • and usages for the 
government of populous settlements living "under the 
ditch," — in short, because they developed permanent 
irrigation agriculture on a community scale, under the 



456 IRRIGATION PRACTICE 

conditions and with the knowledge of modern civilization. 
Irrigation knowledge and inspiration have been drawn 
by the whole world from the work of the first American 
irrigation pioneers. 

The far-reaching consequences of this original experi- 
ment resulted from a combination of conditions not 
before known in irrigation history. The pioneers settled 
in the very heart of the arid section at a time when the 
nearest settlements to the east or to the west were 1,000 
miles away. Starvation or successful agriculture was the 
only alternative offered, since a return to civilization was 
almost impossible to the weary people with worn-out 
equipment. They were compelled to make irrigation 
successful. Then, they were wholly unfamiliar with 
irrigation practices. True, they were men and women of 
good intelligence and information, and knew the place of 
irrigation in the world's history; some of them also had 
probably seen, in their native New England, the occa- 
sional irrigated meadow; but, they had no real knowledge 
of irrigation as the central idea of agriculture. They 
were, therefore, unhampered by traditional irrigation 
practices, and built from the foundation as their needs 
and intelligence directed. Moreover, these irrigation 
pioneers were of the race that had carried onward modern 
civilization; of a country with huge courage to achieve 
great tasks, and of a day when new and increasing truth 
rendered easier the work of man. They founded their irri- 
gation, therefore, in vision and with modern intelligence. 
Naturally, under such conditions, the system of irrigation 
that arose in the heart of the Great American Desert was 
modern and original in method and application, and be- 
came a system to which modern man, interested in the 
conquest of the desert, has since looked for help. 



THE HISTORY OF IRRIGATION 457 

263. The growth of American irrigation. — The original 
irrigation pioneers of July 24, 1847, numbered 147; in 1865, 
nearly 64,000 souls were living in Utah and were deriving 
their main sustenance from irrigation. During these 
eighteen years more than 1,000 miles of irrigation canals 
had been constructed, another 500 miles were being 
dug, and 154,000 acres of cultivated land were under 
irrigation. 

In 1865 the average acre-yield of wheat was 23 bushels; 
of barley, 30 bushels; of oats, 31 bushels; of corn, 20 bush- 
els; of potatoes, 139 bushels; of beets, 265 "bushels;" of 
carrots, 344 "bushels;" of meadow hay, l%tons; of cotton, 
151 pounds; and of sorghum, 79 gallons. Considering 
that the rapidly arriving farmers had to be taught irri- 
gation, and were provided with poor machinery, these 
yields showed the great possibilities of irrigation. 

Soon after the founding of irrigation in the Great Salt 
Lake Valley, gold was discovered in California. Most of 
the tens of thousands who nocked to the gold-fields passed 
through Utah and Salt Lake City and thus became in a 
measure acquainted with irrigation. Many of these 
emigrants, upon their arrival in California, found irrigation 
agriculture more profitable than gold-hunting. Others, 
rich or discouraged, returned to their homes in the East, 
and told not only of the gold-fields, but of the conversion 
of the heartless desert into a fruitful garden by the intelli- 
gent will of a courageous people. The stories of the trav- 
elers gained currency until the whole country knew a little 
of the practice and possibilities of irrigation in the Great 
West. Moreover, big-visioned men, like Major J. W. 
Powell, and his great associates on the United States 
Geological Survey who had explored the arid region, or 
like Horace Greeley, who had carefully informed himself, 



458 IRRIGATION PRACTICE 

spoke and wrote of the great opportunities of the West 
under irrigation. 

However, the year 1870 was almost reached before 
the American people began to give serious attention to the 
irrigable West, so strange and forbidding did irrigation 
seem to the rainfall farmers. With the opening of the 
'70's came a slight change of heart. Many colonies were 
established, and with every year the emigration increased. 
In 1878, Major J. W. Powell's report on the arid lands was 
published by the government. The public interest became 
aroused. The westward movement was already covering 
the Great Plains, and overflowing steadily into the region 
where irrigation was at that time generally held to be 
indispensable. All classes of people discussed the Great 
West as a great hope of the Republic. 

From 1870 to 1880, the population of the mountain 
states doubled; from 1880 to 1890, it almost doubled 
again. The future of irrigation was safe. Then, the cau- 
tious men of money thought their opportunity had come. 
Great sums were spent in building splendid canals above 
fertile lands, with the thought that the farmers who settled 
below the canal would pay a royal annual tribute for the 
water delivered to the land. But the process of settling 
a new country is slow; irrigation succeeds best under a 
close social and economic organization in which canal- 
owner and water-user must be equal members, and the 
West is large; so, in face of the slow adjusting of difficulties 
and the slower settlement of the projects, capital often 
became discouraged and surrendered its property at a loss 
rather than to await the sure harvest that the years would 
bring. Occasionally, also, as in all enterprises, the careless 
or dishonest or ignorant speculator appeared and for a 
time misled both capital and farmer. 



460 IRRIGATION PRACTICE 

Soon after 1890, the era of the irrigation speculator 
ended. The development of irrigation continued un- 
diminished, but along safe and legitimate lines. Legis- 
lation by state and federal governments (such as the 
Carey Act) encouraged sane irrigation progress. Western 
Canada, lying under the same general conditions as 
western United States, joined vigorously in the movement, 
constructed canals and opened fertile lands for settlement. 
Finally, the greatest irrigation experiment of modern 
days was officially declared successful when the Congress 
of the United States in 1902 passed the great reclamation 
act. 

The irrigation structures existing in the United States 
in 1910 irrigated nearly 14,000,000 acres, and could irri- 
gate nearly 20,000,000 acres. All this has been done 
since 1847; and the work, still going on, is far from 
being finished. 

264. The Union Colony of Colorado. — This colony, 
which in 1870 founded Greeley, Colorado, is next to the 
Utah settlement the most important in the history of 
American irrigation, for it also established the practice 
on a community scale and demonstrated the essential 
correctness of the methods of the Utah pioneers. The 
colony was organized on the cooperative plan by N. C. 
Meeker, who had earlier in life belonged to cooperative 
settlements and who had also become familiar with the 
Utah method of settlement. The members of the enter- 
prise were men and women of a high order of intelligence 
and ideals, who carried onward the cooperative spirit. 
The early success of the colony, upon which the later 
success rests firmly, may be credited to the union feature. 
It has been observed that all irrigation enterprises in 
which many families draw support from one ditch or 



THE HISTORY OF IRRIGATION 461 

system of ditches become more successful as the coope- 
rative spirit grows. Other colonies were soon founded 
near and in imitation of the Union Colony, as, for instance, 
the Chicago Colony at Longmont, the Fountain Colony 
at Colorado Springs, the Agricultural Colony at Fort 
Collins, and the Southwestern Colony at Green City. 
The work of these colonies helped to place on a sounder 
basis the practice of irrigation in the United States, and 
made of northeastern Colorado one of the most famous 
agricultural districts of the country. 

The Union Colony, with its outgrowths, is entitled to 
the credit of being associated with the first serious at- 
tempts to measure and distribute water accurately for 
irrigation. In this part of Colorado, also, were suggested 
and initiated many of the systematic investigations of the 
conditions determining successful irrigation. Many famous 
names are connected with the struggles of the Colorado 
irrigation pioneers, originating with the Union Colony of 
1870. The Colorado experiments confirmed the Utah 
experience. 

265. The United States Reclamation Service. — During 
the first fifty years of irrigation in the United States, the 
Federal government gave little direct assistance to the 
reclamation of arid lands beyond the enactment of laws 
that made the public domain readily available to the 
settler. As the public lands under large rainfall passed 
into private ownership, and the demand for homesteads 
continued, Congress gave consideration to federal aid to 
irrigation, and on June 17, 1902, nearly fifty-five years 
after the founding of modern American irrigation, passed 
the justly famous reclamation act. 

This act provides that all moneys received from the 
sale and disposal of public lands in all the states west of 



462 IRRIGATION PRACTICE 

and including North and South Dakota, Kansas and 
Oklahoma, excepting the 5 per cent set aside for educa- 
tional purposes, shall be made a "reclamation fund" for 
the "examination and survey for and the construction 
and maintenance of irrigation works for the storage, di- 
vision, and development of waters for the reclamation of 
arid and semi-arid land in the said states." The lands 
brought under irrigation by this act shall be open to 
bona-fide settlers under the regulations of the Secretary 
of the Interior, and at a price that will return in time to 
the reclamation fund a sum equal to that expended by 
the government upon the project. The fund, thus made 
permanent, may continue to serve until all irrigation 
projects feasible under the terms of the act shall have 
been constructed. 

Work under the reclamation act has been pushed 
with vigor almost from the day the act was signed by 
Theodore Roosevelt. The workers have been assembled 
under the head of the United States Reclamation Service, 
the director of which almost from the beginning has been 
F. H. Newell, a life-long student of water supply and 
irrigation, assisted by a most admirable and efficient corps 
of irrigation experts. During its first decade of work, 
the Reclamation Service undertook projects which, when 
completed, will cost over $100,000,000. In 1910 the pro- 
jects of the Reclamation Service irrigated 3 per cent of 
all the irrigated lands in the country, and, when completed, 
would irrigate nearly 7 per cent of the area to be irrigated 
under all projects, private and public. 

Many projects that private enterprise felt unable to 
undertake have been constructed by the Reclamation 
Service. Confidence in the arid section has been strength- 
ened by the national approval of irrigation contained in 



THE HISTORY OF IRRIGATION 463 

the reclamation act. The real problems and possibilities 
of irrigation are being brought home to our national 
leaders by this work as would be possible in no other way. 
It is a great act of endless service to the country. 




Fig. 173. Major J. W. Powell, who, as director of the 
United States Geological and Geographical Surveys, 
was one of the first to understand andteach the value 
of the arid and semi-arid parts of the United States. 

It was fitting that the Interior Department should be 
entrusted with the execution of the reclamation act, for 
it was the Geological Survey that among government 
agencies first studied the beginnings of irrigation in the 
far West, and spoke hopefully of the reclamation of the 



464 IRRIGATION PRACTICE 

Great American Desert. Major J. W. Powell, Director of 
the United States Geological and Geographical Surveys, 
and lover of the West, together with G. K. Gilbert and 
other colleagues, did much to advance the early cause of 
irrigation. Under the direction of the Geological Survey, 
also, with F. H. Newell as hydrographer, the notable 
water-supply papers were issued which laid a foundation 
of knowledge concerning stream flow upon which irri- 
gation plans could be builded. 

266. The United States Department of Agriculture.— 
The building of dams and canals will end, but the use of 
the impounded or diverted water must go on forever. 
Irrigation is essentially an agricultural practice to which 
the civil and mechanical engineers can give only initial 
help. In the earlier days water was plentiful and people 
few, and little water scarcity was felt. The big thing was 
to dig more canals and induce more people to settle under 
the ditch. Now, the question of the best use of the water 
on the land is the big one, because the opportunities are 
fewer, the people more numerous, and those of the arid 
region more determined to build permanently and largely. 
The Department of Agriculture, although somewhat slow 
in sensing the needs of the irrigation farmers, organized 
in 1898 the Irrigation Investigations of the Office of Experi- 
ment Stations, to expend a Congressional appropriation 
"for the purpose of collecting from agricultural colleges, 
agricultural experiment stations, and other sources, 
valuable information and data on the subject of irrigation 
and publishing the same in bulletin form." Elwood 
Mead, already of long and splendid irrigation service, 
was first appointed chief of the Investigations, followed in 
1906 by Samuel Fortier, also with a long and honorable 
irrigation record. In a short time, a series of remarkable 



466 IRRIGATION PRACTICE 

irrigation bulletins appeared, which have continued to 
the present. Doctors Mead and Fortier gathered about 
themselves a body of young able men, who for half a 
generation have been devoting themselves to a study of 
the farmers' side of irrigation. The practices of irrigation 
have been collected and organized; the irrigation systems 
of foreign countries have been studied; experiments have 
been conducted, and in numerous ways the irrigation 




Fig. 175. Steam power digs the modern canals. 

farmer has been given needed help. Not the least of the 
achievements of the United States Irrigation Investi- 
gations has been the encouragement it has given irrigation 
studies at the experiment stations by an intelligent and 
liberal system of cooperative work. 

267. The experiment stations. — Modern agriculture 
was founded in humid regions and, naturally, little 
attention was at first given irrigation. When, however, 
in 1887, an agricultural experiment station was established 
in each of the states and territories, irrigation problems 
presented themselves for solution at most of the western 
stations. E. W. Hilgard, the great man of arid agri- 



468 



IRRIGATION PRACTICE 



culture, had already made observations on Californian 
irrigation for half a generation, but his fundamental soil 
studies had crowded out systematic irrigation experi- 
ments. 

The Colorado and Utah stations were the first to 
undertake special irrigation work. At the Colorado Station, 
among the many workers who gave some attention 




Fig. 177. Dam of Salmon River project, Idaho, built by private enterprise. 

to irrigation, Elwood Mead and, later and chiefly, L. G. 
Carpenter, made classical studies of the measurement, 
division, seepage and underflow of water, together with 
many allied questions. True to its traditional interest in 
the engineering phases of irrigation, the Colorado Station, 
in cooperation with the United States Irrigation Investi- 
gations, completed in 1913 an experimental plant for the 
study of the methods for measuring and dividing water, 
which is unequaled. At the Utah Station, J. W. Sanborn, 



THE HISTORY OF IRRIGATION 



469 



a great pioneer of modern American agriculture, assisted 
by Mills, inaugurated the pioneer investigations of the 
correct use of water on the farm. J. A. Widtsoe, L. A. 
Merrill and others later organized the exhaustive study of 
the relationships existing between soils, crops and water, 
having for its purpose the determination of the most 
economical use of water, which, in new hands, is still 
being continued. The Utah experimental equipment for 





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Fig. 178. Plant for the study of the measurement and division of water. The 
Colorado Experiment Station. 

these investigations was long unique among the stations. 
At the Utah Station, Samuel Fortier also did some of his 
early experimental work, and many members of the station 
staff have conducted investigations bearing more or less 
directly on irrigation. 

The other western stations have all done some excellent 
irrigation work; but the preponderance has been on the 
subject of alkali, rather than on the actual use of water on 
the farm. E. B. Voorhees, of the New Jersey Station, 
studied with care the value of irrigation in humid countries. 



470 IRRIGATION PRACTICE 

The experiment stations have brought forth much 
new irrigation knowledge, and have disseminated widely 
all the sound information existing upon the subject. 
Nearly all the stations in the arid region are now under- 
taking systematic studies having for their purpose the 
establishment of a science of irrigation practice. 

268. The Irrigation Congress. — The reclamation act, 
the land laws making irrigation settlement possible, the 
founding and work of the experiment stations, are all the 
result of the championship of irrigation by clear-headed, 
far-seeing, courageous men, in and out of office, who, in 
legislative halls, from the platform, on the printed page 
and in private conversation, have taught the needs and 
the possible future of irrigation in America. 

These men, whose names are easily forgotten, now that 
the work is done, organized in Salt Lake City the Irrigation 
Congress. The first session was held in September, 1891, 
since when sessions have been held in practically all of the 
irrigation states. Its lists of officers during these many 
years include the names of the irrigation leaders of America 
— names of national renown for great service rendered. 
The proceedings of the Congress developed and sustained 
the enthusiasm which has made irrigation a national 
issue. No doubt the Irrigation Congress made possible 
much of our recent irrigation progress. Now that reser- 
voirs and canals are being rapidly built and irrigation has 
been firmly established, the mission of the Congress looms 
larger than ever — to make systematic, profitable and per- 
manent the use of the water upon the land. 

Major Richard W. Young, a grandson of the founder 
of modern irrigation in America, is the present President 
of the Irrigation Congress. The Congress for 1914 will be 
held in the province of Alberta, Canada. 



THE HISTORY OF IRRIGATION 471 

REFERENCES 

Powell, J. W., with Gilbert, G. C., Dutton, C. E., and Thomp- 
son, A. H. The Lands of the Arid Region of the United States. 
United States Department of the Interior (1878). 

United States Department of State. Canals and Irrigation in 
Foreign Countries. Special Consular Reports, Vol. V (1898). 

Gray, E. D. McQueen. Government Reclamation Work in Foreign 
Countries. United States Government Printing Office (1909). 



CHAPTER XXII 

PERMANENT AGRICULTURE UNDER 
IRRIGATION 

"The desert shall blossom as the rose," said the 
ancient prophet; and a modern man, witnessing the ful- 
fillment, by irrigation, of the ancient prediction, was so 
wrought upon by the transformation of desert into garden 
that he declared it a miracle. Later, another man, per- 
ceiving clearly the permanency of the work, declared that 
irrigation is a continuous miracle. That was nearer the 
truth. Today, with our greater understanding, irrigation 
is less of a miracle; it is more of an intelligent conquest — 
a continuous conquest of the untoward forces of the desert. 

269. The big irrigation problem. — The word "con- 
tinuous," whether it be of miracle or of conquest, lingers, 
for it expresses the essence of the virtue of irrigation. 
The mountain stream or the sluggish river, once brought 
through reservoir and canal upon the desert land, will 
make that land yield in plenty and in beauty, not for a 
generation or two, but, if man so decrees, during the 
coming ages of the earth — at least while climatic con- 
ditions remain unchanged. Therefore is the builder of 
the irrigation canal a master-builder. 

The battle for recognition has been fought and won. 
Arid and humid regions look to irrigation as one of the 
chief weapons with which to conquer drought and to 
make the land yield richly. Private capital and public 
funds vie with each other for the privilege of fostering 

(472) 



AGRICULTURE UNDER IRRIGATION 473 

irrigation. It seems certain that as soon as sound growth 
will allow all the water, especially in the arid regions, will 
be stored and diverted for purposes of irrigation. 

The mighty dams and endless lines of canals will soon 
be completed. If the work has been well done, we shall 
need only to maintain in a sound condition the structures 
of steel and rock and cement and wood and earth that 
have been built. The overshadowing problem then, as it 
is the great one now, will be that of using the water in 
the best manner for the production of crops. Two- 
headed is this problem: First, the water must be made to 
produce the largest total yield of crops for the support of 
man; second, the practice of irrigation on a given area of 
land must be made continuous and increasingly desirable. 
To this double problem is this volume devoted. 

270. The spirit of irrigation. — Our modern knowledge 
is teaching the methods whereby irrigation may be made 
to produce the maximum crops for each unit of water used. 
All irrigation advocates are rapidly accepting the new 
truth. The very spirit of the conquest of the desert is 
that men shall be benefited — many men; the more men 
the better. The largest possible area of land must be 
reclaimed by the stored waters, even if the acre-yield 
does not reach so high an average. 

271. No essential difference between irrigation- and 
humid-farming. — Our modern knowledge teaches also 
that there is no essential difference between rainfall- 
farming and irrigation-farming, except in the manner in 
which water is applied to the soil. Every argument against 
the permanency of irrigation-farming may be urged 
against rainfall-farming; and every argument for the per- 
manency of rainfall-farming may be used with equal force 
in behalf of irrigation-farming. The everlasting relation- 



474 IRRIGATION PRACTICE 

ships among soils, waters and plants are the same over all 
the earth. Under irrigation, the great water factor may 
be controlled, and thereby greater power for good or for 
evil is possessed by the farmer under the ditch. 

Yet there are some who, while admitting the great 
present value of irrigation, fear that in it is an element of 
weakness which will make the practice temporary. 

272. History assures permanence of irrigation. — A 
sufficient answer may be the history of the past. As shown 
in the preceding chapter, great tracts of lands are known 
that have been farmed successfully, under irrigation, dur- 
ing the last 2,000 to 4,000 years and are today as pro- 
ductive as ever. In fact, the human race was cradled and 
grew to maturity in irrigated countries. That some of 
the great nations of antiquity crumbled to dust was not 
because they dwelt on irrigated lands; their fall was 
rather delayed because of the bounteous yields of their 
irrigated fields; and, in truth, the fallen nations of the 
past practised irrigation for so long — often for thousands 
of years — that the permanent nature of this branch of 
agriculture was well demonstrated before the shifting 
scenes of history brought new lands and other peoples 
into emphatic view. 

273. The question of plant-food. — The fertility of the 
soils must be carefully guarded under irrigation as under 
rainfall. When moderate quantities of water are used no 
more plant-foods are washed away than under an equiva- 
lent rainfall. Instead, the deep, rich soils of the arid re- 
gions, because of the possible water storage in them, can 
better retain the essential elements of plant-food. During 
the course of modern American irrigation, extending over 
two-thirds of a century, the average productive power of 
the irrigated lands has steadily increased. Against the 



AGRICULTURE UNDER IRRIGATION 



475 




Fig. 179. Work for a man. Irrigation requires strength of body, good intelligence 
and sound and rapid judgment. 

fifteen or twenty bushels of wheat per acre harvested in the 
first years of irrigation, forty to fifty bushels are now 
harvested on the same lands. True, this must be due 
chiefly to improved methods of culture, with modern 
tools, but certainly there is in this record no sign of 
deterioration. 



476 IRRIGATION PRACTICE 

274. Some advantages of irrigation. — There are many- 
reasons why irrigation-farming should become and remain 
very attractive. Under irrigation, crop-yields may be 
depended on from year to year. Crop failures are very 
rare and are usually due to hail- storms or some unusual 
atmospheric disturbances. The possibility of varying the 
quantity of water applied to the land gives the farmer a 
control over the yield and quality of the crop that does 
much to vitalize the routine of the work and to make the 
harvest more profitable. The soil and climatic conditions 
prevailing over most of the territory demanding irrigation 
are of a kind to make life enjoyable. 

275. Finally. — The nature of irrigation is such as to 
bring into close social relationship the people living under 
the same canal. A common interest binds them together. 
If the canal breaks or water is misused, the danger is for 
all. In the distribution of the water in the hot summer 
months when the flow is small and the need great, the 
neighbor and his rights loom large, and men must gird 
themselves with the golden rule. The intensive culture, 
which must prevail under irrigation, makes possible close 
settlements, often with the village as a center. Out of 
the desert, as the canals are dug, will come great results 
of successful experiments in intimate rural life; and out 
of the communities reared under irrigation will come men 
who, confident that it is best, can unflinchingly consider 
their neighbors' interests with their own; and who, there- 
fore, can assume leadership in the advancing of a civili- 
zation based upon order and equal rights. 

The environment of wise irrigation-farming compels 
the belief that of all kinds of farming it may be the most 
enduring. 

King, F. H. Farmers of Forty Centuries (1911). 



APPENDIX A 
WATER CONSTANTS 

Chemical formula for water = H 2 0. 

Specific gravity of water = 1. 

Maximum density of water occurs at 4° C. or 39.2° F. 

1 cubic foot of water at 4° C. =62.2786 pounds. 
1 cubic foot of water at 49° F. =62.2515 pounds. 
1 gallon (U. S.) of water = 8.3254 pounds. 
1 cubic foot of water = 7.48 gallons. 
1 litre of water = 2.1997 pounds. 
1 ton = 32.1 cubic feet of water. 

1 acre-foot = the volume of water which will cover an acre 1 foot deep. 
1 acre-inch = the volume of water will cover an acre 1 inch deep. 
1 acre-foot = 43, 560 cubic feet. 
1 acre-foot = 2,712,856 pounds. 

1 California "miner's inch" =0.020 cubic feet per second. 
1 Colorado "miner's inch" =0.026 cubic feet per second. 
1 Arizona "miner's inch" =0.025 cubic feet per second. 

1 cusec = 1 second-foot = 1 cubic foot of water per second. 

1 second-foot flowing for twenty-four hours ( = 86,400 cubic feet) 
will cover 1 acre 1.9835 feet deep = 1.9835 acre-feet (approxi- 
mately 2 feet). 

1 second-foot flowing for 120 days will cover: 

240 acres 1 foot deep. 120 acres 2 feet deep. 

180 acres 13^ feet deep. 80 acres 3 feet deep. 



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(483) 



APPENDIX C 

The following brief list gives the titles of the few books on irri- 
gation for the farmer published in the United States : 

Anderson, D. H. Primer of Irrigation. D. H. Anderson Publish- 
ing Company, Chicago (1903). 

Bowie, A. J. Practical Irrigation. McGraw Publishing Com- 
pany (1908). 

King. F. H. Irrigation and Drainage. The Macmillan Company, 
New York (1899). 

Mead, Elwood. Irrigation Institutions. The Macmillan Company, 
New York (1903). 

Newell, F. H. Irrigation. T. Y. Crowell & Co., New York (1902). 

Olin, W. H. American Irrigation Farming. A. C. McClurg & Co., 
Chicago (1913). 

Smythe, W. E. The Conquest of Arid America. The Macmillan 
Company, New York (1905). 

Stewart, Henry. Irrigation in Field and Garden. Orange Judd 
Company, New York (1886). 

Wilcox, Lucius M. Irrigation Farming. Orange Judd Company, 
New York (1902). 



(484) 



INDEX 



Abraham, 446. • 

Absolute duty of -water, 335. 

Absorption by soils, 76. 

of water by roots, 109, 

effect of initial percentage, 111. 
Adams, 368, 369. 
Advantage of irrigation, 476. 
Africa, duty of water in, 338. 

use of saline water in, 387. 
Agricultural Colony, 461. 
Alfalfa, 152. 

See also Lucern. 

time of watering, 186. 

protein in, 221. 

yield due to rainfall, 234. 

under irrigation, 266. 

cultivation of, 268. 

method of irrigation, 269. 

time of irrigation, 270. 

quantity of water for, 274. 

duty of water, 344. 
Alfalfa seed, 277. 
Algeria, 83. 

Alkali. See also Over-irrigation and 
Seepage, 371. 

drainage from a soil, 78. 

upward leaching, 81. 

use of concentrated water, 89. 

defined, 383. 

and seepage, 384. 

upward leaching, 385. 

use of saline water, 387. 

deposits, 388. 

kinds, 390. 

white, brown and black, 392. 

plant tolerance for, 392. 

tolerance of various plants, 394. 

tolerance according to Bureau of 
Soils, 395. 

cropping against, 397. 

chemical treatment for, 398. 

tillage against, 399. 

scraping against, 399. 

washing out, 400. 

drainage, the remedy, 400. 
Almonds, spacing of, 317. 
Alway, 39. 



Amazon, 84. 

America, founding of modern irrigation, 

454. 
Ames, Iowa, 407. 
Anderson, 405. 
Anderson, D.H., 484. 
Anglo-Saxon irrigation, 452. 
Apples, protein in, 221. 

duty of water for, 322. 

sugar in, 225. 

spacing, 317. 
Application, distribution on, 364. 
Apricots, spacing, 317. 
Argentina, 453. 
Arizona Station, 179. 
Arkansas River, 83. 
Artesian water, 410. 
Ash constituents. See also Plant-food 

in plants, 219. ' 

Asia,- duty of water in, 339. 
Asparagus, under irrigation, 309. 
Assam, India, rainfall at, 2. 
Assimilation of carbon by plants, 128, 

129. 
Assuan, 338, 452. 
Assyria, 445. 
Atlanta, 408. 

Attraction of near bodies, 8. 
Australia, 453. 

duty of water expression, 331. 

duty of water in, 343. 
Australia n saltbush , alkali - resistant , 
397. 

Babylon, 445. 

Bacteria, soil, and water, 104. 

Bark, 234, 248, 249, 264, 273, 284, 345, 

369. 
Barley, under irrigation, 255. 

duty of water, 344. 

alkali-resistant, 396. 

in humid climates, 411. 

early yield, 457. 
Barri-Doab Canal, 341. 
Bartlett, 405. 
Basin irrigation, 207. 
Beans under irrigation, 301. 



(485) 



486 



INDEX 



Bear River, 83. 

Bear River Canal, duty of water, 253, 

344. 
Beckett, 63, 215. 
Beets, early yield, 457. 
Bell, 106. 

Belle Fourche River, 96. 
Belz, 44, 63. 
Bennett, 329. 
Bighorn River, 96. 
Billings, Mont., 78. 

alkali experiment, 402. 
Blackberries, 326. 

protein in, 221. 

sugar in, 225. 

in humid climates, 410. 
Bond, 264. 
Bonsteel, 403. 
Border irrigation, 202. 
Bouyoucos, 118, 125, 156. 
Bowie, 409, 417, 484. 
Breaking land, 419. 
Briggs, 20, 44, 63, 126, 156. 
Brome-grass, 278. 
Brown, 403. 
Buckingham, 51, 52, 63. 
Buckley, 340, 369. 
Buds affected by irrigation, 320. 
Buergerstein, 126. 
Burke, 403, 405. 
Burr, 39. 

Cabbage under irrigation, 308. 
Cache la Poudre River, 83. 
California, 457. 

flooding irrigation in, 315. 

duty of water in, 323. 

lined ditches in, 378. 

rivers, 84. 
California station, 15, 30. 
Cameron, 48, 63, 66, 68, 70, 106, 387, 

392. 
Campbell, 62, 239. 
Canals, loss from Indian, 341. 

seepage from, 371. 
Cantaloupe, 171. 

under irrigation, 306. 
Canvas dam, 438. 
Canada, 460. 

rivers, 85. 

duty of water expression, 331. 

irrigation in, 339. 
Cape Colony, 339, 453. 
Capillarity. See Soil moisture, Soils, 
Water. 

maximum capacity, 17. 
Carbohydrates in plants, 224 



Carbon, assimilation by plants, 128, 

129. 
Carey Act, 460. 
Carpenter, 352, 369, 372, 374, 403, 449, 

468. 
Carrots, time of irrigation, 185. 
under irrigation, 296. 
early yield, 457. 
Catholic Fathers, 451. 
Cauliflower under irrigation, 308. 
Cavour Canal, 452. 
Celery under irrigation, 309. 
Cement concrete, as ditch-lining, 377. 
Cereals, irrigation of, 240. 
Ceylon, 446. 
Chalis River, 83. 
Check irrigation, 202. 
Checks for ditches, 434. 
Cherries, protein in, 221. 
sugar in, 225. 
spacing, 317. 
Chicago Colony, 461. 
Chili, 447. 

duty of water in, 342. 
China, 416, 446. 
Cincinnati, 408. 
Cippoletti's weir, 352. See also Weir. 

discharge over, 478. 
Citrus trees under irrigation, 321. 
duty of water for, 322. 
water requirements, 323. 
Clark, 39, 312. V 
Clarke, 83, 90, 106. 
Clearing land, 419. 
Clover, red, under irrigation, 281. 

in humid climates, 411. 
Coburn, 284. 
Coit, 312, 327, 329. 
Collins, 106. 
Color of plants, 227. 
Colorado, time of irrigation in, 320. 

alkali from, 391. 
Colorado River, 96. 
Colorado Station, 355, 468. 
Colorado Springs, 461. 
Columbia, S. C, 407. 
Colver, 170, 230. 

Composition, effect of tillage on, 228. 
Cone, 369. 
Connecticut, 411. 
Constants for water, 477. 
Continuous flow, for distribution, 358. 
Continuous rotation, for distribution, 

361 
Cooking value of plants, 228. 
Corbet, 312. 
Corn, transpiration, 60. 



INDEX 



487 



Corn, time of irrigation, 185. 

protein in, 221. 

yield due to rainfall, 234. 

under irrigation, 255. 

cultivation of, 256. 

yield with varying water, 256. 

time to irrigate, 258. 

quantity of water for, 259. 

in humid climates, 410, 411. 

early yield, 457. 
Cotton, early yield, 457. 
Council Bluffs, 454. 
Craigentinny, 415. 
Cranberries, 326. 
Crane, 410. 
Crawley, 29. 
Crop. See also Plant. 

development under irrigation, 158. 

time to irrigate short-season crops, 
183. 

composition, 216. 

use of rainfall in production, 231. 

value of rainfall in irrigation, 233. 

tolerance of various, for alkali, 394. 

yields under early irrigation, 457. 
Crowder, 428. 
Cultivation. See also Mulching. 

saving water by, 40. 

against evaporation, 49. 

time, 53. 

depth, 55. 

frequency, 58. 

and soil fertility, 59. 

effect on water use, 121. 

in dry-farming, 237. 

of wheat, 243. 

of corn, 256. 

of alfalfa, 268. 

of sugar beets, 288. 

tools for, 440. 
Cultivator, with shovel attachment, 

439. 
Cultural operations, effect on water- 
cost, 141. 
Currants, 326. 

in humid climates, 410. 
Cusec defined, 332. 
Cushman, 106. 

Dammer, 437. 
Danube, 97. 
Date, 314. 

under irrigation 328. 

alkali-resistant, 396. 
Davis and Weber Counties Canal, 366, 

378. 
Day irrigation, 187. 



Dead Sea, 83. 

Definition of irrigation, 4. 

Denver, 408. 

Desert, rainfall on, 1. 

Dewberries, sugar in, 225, 326. 

Distribution of water, 357. 

methods, 358, 361, 364. 

organization for, 365. 

cost of, 267. 

regulations and records, 368. 
Ditch, concrete, 197. 

lined, against seepage, 376. 

locating, 420, 421. 

permanent, 196. 

typical farm, 425. 

making, 426. 

discharge of various, 432. 
Ditch-tenders, for water distribution, 

367. 
Divisors, 350, 355. 
Dole, 106. 
Dorsey, 403. 
Drainage-water, composition of, 78. 

loss of plant-food, 79. 

of wet lands, 381. 

remedy for alkali, 400. 
Drill, in sowing wheat, 242. 
Droughts, 407. 
Dry-farming, 231. See also Rainfall. 

conditions of, 3. 

mission of, 7, 231. 

defined, 233. 

results of, 233. 

cultivation, 237. 

relation to irrigation, 237. 

homesteads for, 238. 

mission of, 239. 

Congress, 239. 

orchard experience, 324. 
Dry-matter. See also Water-Cost. 

water-cost of, 127. 
Duty of water for 

wheat, 248, 252, 253. 

oats, 253. 

barley, 255. 

rye, 255. 

corn, 259. 

rice, 263. 

alfalfa, 274. 

hay crops, 278. 

clover, 281. 

pastures and meadows, 281. 

sugar beets, 293. 

carrots, 297. 

potatoes, 299. 

peas and beans, 301. 

fiber crops, 305. 



488 



INDEX 



Duty of water for 

hops, 306. 

tomatoes, 306. 

watermelons, 307. 

squash, 307; pumpkin, 307; egg- 
plant, 307. 

cantaloupes, 307. 

cabbage, 308. 

'cauliflower, 308. 

spinach,308; lettuce,308; parsley,309. 

asparagus, 309; for celery, 309. 

onions, 310. 

rhubarb, 310; tobacco, 310; peanuts, 
310. 

orchards, 322. 
Duty of water. 

defined, 331. 

common meaning, 332. 

classes of, 334. 

formula for, 334. 

difficulty of determining, 336. 

and profit from crops, 337. 

cause of differences in, 338. 

in Africa, 338. 

in Asia, 339. 

in Europe, 341. 

in South America, 342. 

in Australia, 343. 

in North America, 343. 

under Bear River Canal, 344. 

miscellaneous results, 345. 

in Idaho, 345. 

Utah Station results, 346. 

the new duty, 347. 

in humid climates, 413. 

Eaton, 106. 

Economical irrigation, wheat, 252. 

against seepage, 381. 
Edinburgh, 415. 
Eggplant under irrigation, 307. 
Egypt, 445, 452. 

duty of water in, 338. 
Elbe, 84. 
Elliot, 403. 
Etcheverry, 329, 403. 
Europe, duty of water in, 341. 
Evans, 284, 285. 
Evaporation and loss of soil moisture,43. 

intensity, 44. 

conditions determining, 46. 

mulching against, 49. 

effect of rolling, 62. 

conditions determining use of water 
by plants, 108. 
Evapo-transpiration ratio, 132. 
Experiment stations, 466. 



Factory waste, 417. 
Fall irrigation, 175. 

time of application, 177. 
Farmers' Canal, 366. 
Fat in plants, 223. 
Fiber crops under irrigation, 305. 
Field-ditch irrigation, 198. 
Field-lateral irrigation, 198. 
Field moisture-capacity, 29. 
Fippin, 13. 
Fitterer, 404. 
Flavor of plants, 227. 
Flax and alkali, 398. 
Fleming, 403. 
Flour composition of, 227. 
Flynn, 369. 

Forage crops under irrigation, 266,278. 
Forbes, 101, 106. 
Fort Collins, 461. 

Fortier, 46, 48, 49, 63, 156, 215, 239, 
274, 284, 322, 329, 343, 344, 404, 
444, 464, 466, 469. 
Fountain Colony, 461. 
France, 450, 451. 

duty of water in, 342. 
Free water, 17. 

Fresno, alkali experiment, 402. 
Fruit. See also Orchard. 

composition, 171. 

quality under irrigation, 225. 
Fruit-growing. See also Fruits, Orchard. 

under irrigation, 314. 
Furrow-irrigation, 207. See also Method 

of Irrigation. 
Furrowing, tools for, 439. 
Fuller, 403. 

Gage Canal, 366. 

Gain, 162. 

Gallagher, 66, 68, 70, 106. 

Gates for ditches, 434. 

Genii, 450. 

Gilbert, 133, 464. 

Gooseberries, 326. 

in humid climates, 410. 
Grains. See also Cereals. 

proportion of grain, 166. 

time of irrigation, 183. 

irrigation of, 240. 

destiny of grain-farming, 241. 

duty of water in Africa, 339. 
Grant-Mitchell meter, 442. 
Grapes, protein in, 221. 

sugar in, 225. 

under irrigation, 327. „ 

Gray, 471. 
Gravel, 34. 



INDEX 



489 



Greasewood, 397. 
Great Basin rivers, 84. 
Great Britain rivers, 84. 
Great Plains, 458. 
Great Salt Lake, 83, 389. 

alkali experiment, 401. 

water, 91. 
Great Salt Lake Valley, 455. 
Greaves, 105, 106, 405. 
Greeley, 457. 
Greeley, Colo., 460. 
Green City, 461. 
Greenhouse irrigation, 192. 
Green River, 98. 
Gross duty of water, 335. 
Ground- water, 373. 
Growth, conditions of plant, 130. 
Grubb, 312. 
Guilford, 313. 
Gunnison River, 96. 

Hammurabi, 446. 

Hanksville, Utah, 324. 

Hardpan, 30. 

Hare, 106. 

Harris, 146, 156, 172, 187, 264, 405. 

Hawaii, 29,411. 

Hay, time of irrigation, 186. 

crops under irrigation 278. 
Headden, 404. 
Head of water, 194. 

proportion of, 166. 
Hellriegel, 133, 167 
Henry, 7. 
Herrick, 329. 

Hilgard, 20, 106, 239, 393, 398, 404, 466. 
Homesteads on dry-farms, 238. 
Hood River Valley, time of irrigation 

to, 320. 
Hops under irrigation, 306. 
Horton, 369. 
Hirst, 230. 

History of irrigation, 445. 
Humbert, 157, 264. 
Humid climates, irrigation in, 406. 

results of irrigation in, 409. 
Hunt, 264. 
Hygroscopic coefficient, 13. 

Idaho, time of irrigation in, 320. 

duty of water in, 345. 
Imperial Valley, 327. 
India, 446, 452. 

duty of water expression, 331. 

duty of water in, 339. 

duty of water, 341. 
India rivers, 84. 



Initial percentage, effect on evapora- 
tion, 48. 

effect on use by plants, 111. 
Interculture of orchards, 323. 
Irrigation. See also Time, Method, 
Quantity of Irrigation. 

defined, 4, 231. 

conditions, 4. 

extent of, 5. 

need of, 5. 

mission of, 7. 

intermittent practice, 21. 

response to, 159. 

supplementary to rainfall, 231. 

crop value of rainfall in, 233. 

relation to dry-farming, 237 . 

for dry-farm homesteads, 238. 

mission of, 239. 

engineer to measure water, 349. 

engineer for water distribution, 366. 

in humid climates, 406. 

results in humid climates, 409. 

history of, 445. 

antiquity of, 445. 

during Christian era, 449. 

in recent times, 451. 

Congress in British South Africa, 
453. 

modern founding in America, 454. 

permanent agriculture under, 472. 

the big problem, 472. 

spirit of, 473. 

difference between arid and irriga- 
tion farming, 473. 

history assures permanence of, 474. 

social condition of, 476. 

advantages of, 476. 
Irrigation Congress, 470. 
Irrigation Engineer. See Irrigation; 

Water Master. 
Italy, 450. 

duty of water in, 342. 

Java rivers, 84. 
Johnston, 444. 
Jones, 170, 224, 230. 
Jordan River, Utah, 83 
Joseph, 445. 

Kafir corn, alkali-resistant, 396. 
Kearney, 387, 392, 404. 
Keeney, 264. 
Kennedy, 341. 
Khankhaje, 156. 
Kiesselbach, 156. 

King, 14, 20, 76, 106, 133, 156, 411, 
415, 418, 476, 484. 



490 



INDEX 



Kneale, 405. 
Knight, 390. 
Kraus, 230, 329. 

Lake waters, salinity of, 86. 
Lateral organization, 367. 
Lath-boxes, 212. 
Laying-out farm, 420. 
Lay-off, 440. 

in furrow irrigation, 209. 
Lawes, 133. 

Leaching upward, 81, 385. 
Leather, 39, 133, 134, 136, 156. 
Leaves, proportion of, 163. 
Le Clerc, 230. 

Legumes, not alkali-resistant, 398. 
Lemon, 314. 

Lento-capillary point, 16. 
Lettuce under irrigation, 308. 
Leveling land, 423. 
Lewis, 230, 326, 329. 
Loganberries, 326. 
Lombardy, 450. 

sugar in, 225. 
Longmont, 461. 
Longyear, 329. 

Loughridge, 30, 39, 215, 392, 393, 404. 
Lucern. See Alfalfa. 
Lyman, 352, 369. 
Lyon, 13, 146. 
Lysimeter, 77. 

Macdonald, 239. 

Manager for water-distribution, 366. 

Manuring effect on water-use, 121. 

Manufactured crops, importance of, 266. 

Marking, in furrow irrigation, 208. 

Mawson, 339. 

Maxwell, 411 418. 

Mayer, 156, 145, 167. 

McClatchie, 179, 188, 239, 404. 

McDowell, 188. 

McLaughlin, 20, 39, 63, 126, 248, 264, 

284, 313. 
McKee, 285. 
Mead, 7, 215, 239, 343, 346, 369, 404, 

418, 464, 466, 468, 484. 
Meadow hay, early yield, 407 
Meadows under irrigation, 281 
Means, 404. 
Measurement of water. See also Weir. 

Instruments for, 441. 

need of, 347. 

classes of measurements, 349. 

who shall measure, 349. 
Meeker, 460. 
Mehemet Ali-Pasha, 452. 



Menes, 445. 

Merrill, 188, 215, 265, 239, 285, 313, 

370, 469. 
Meteorology, effect on evaporation, 44, 

47. 
Method of irrigation, 189. 

sub-surface irrigation, 189. 

permanent ditches, 196. 

open and closed fields, 196. 

field-ditch or lateral method, 198. 

check method, 202. 

border method, 202. 

furrow method, 207. 

basin method, 207. 

summary of methods, 214. 

of wheat, 243. 

of alfalfa, 269. 

of sugar beets, 289. 

of orchard, 315. 

in humid climates, 412. 
Mexico, 447. 
Milan, 408, 415. 
Mill waste, 417. 
Mills, 468. 

Mineral oil, as ditch-lining, 377. 
Miner's inch, 332. 
Mitchell, 106. 
Modules, 350. 

Moisture in soil. See Soil Moisture. 
Montgomery, 156. 
Moors, 449. 
Morgan, 146, 157. 
Morgan, E. R., 264, 278, 284, 313. 
Mormon pioneers, 455, 201. 
Mulching. See Cultivation. 

to check evaporation, 49. 

self-mulching soils, 52. 

Nebraska Station, 37. 

Net duty of water, 335. 

Newell, 7, 346, 369, 462, 464, 484. 

New England, 406. 

New Jersey, 410. 

New Jersey Station, 469. 

New Mexico, alkali from, 391. 

Night irrigation, 187. 

Nile, 84, 85, 97, 104, 339, 445. 

Nitrogen. See Protein. 

North America, duty of water in, 343. 

North Platte River, 96. 

Nowell, 264, 313. 

Nursery stock, under irrigation, 326. 

Nuts, 314. 

Oats, ash in leaves, 219. 
ash in stalks, 219. 
protein in, 221. 



INDEX 



491 



Oats, yield due to rainfall, 234. 

under irrigation, 253. 

duty of water for, 253. 

early yield, 457. 
Ocean water, 91. 

composition, 92. 
Office of Experiment Stations, 464. 
Olin, 484, 285. 

Olive, duty of water for, 322. 
Omaha, 408. 
Onions under irrigation, 310. 

in humid climates, 410. 
Orange, 314. 

spacing, 317. 
Orchard. See also Fruit-growing. 

time of fall irrigation, 177. 

time to irrigate, 187. 

furrowing, 210. 

under irrigation, 314. 

method of irrigation, 315. 

care of young, 315. 

furrows for young trees, 317. 

time of irrigation, 319. 

effect of irrigation on buds, 320. 

quantity of water for, 322. 

danger of over-irrigation, 323. 

inter-culture, 323. 

growth without irrigation, 324. 

duty of water in Africa, 339. 
Orchard-grass, 278. 
Organization, for distribution, 365. 
Ornamental Plants under irrigation 

328. 
Oshkosh, Wis., 407. 
Overfalls, 351. 

Over-irrigation, 371. See also Seepage, 
Alkali. 

delays ripening, 251. 

danger in orchards, 323. 

water-loss from, 373. 

Packard, 312, 329. 

Packing, natural, of soil, 70. 

Paddock, 329. 

Palestine, 446. 

Palmer, 224. 

Pastures under irrigation, 281. 

Patten, 71, 106. 

Peach, protein in, 221. 

sugar in, 225. 

spacing, 317. 
Peanuts, 310. 
Pears, protein in, 221. 

spacing, 317. 

duty of water for, 322. 
Peas, protein in, 221. 

under irrigation, 301. 



Pecos River, 96. 
Pennsylvania, 409. 

Permanence of irrigation agriculture, 
472. 

of irrigation assured by history, 474. 
Persia, 446. 
Peru, 447. 

duty of water in, 342. 
Peterson, 390. 
Phelps, 411, 418. 
Phoenix, 408. 
Pinckney, 403. 
Plant. See also Crop. 

use of soil moisture by, 108. 

absorption of water by plant-roots, 
109. 

initial percentage and water use, 111. 

effect of water distribution on water 
use, 114. 

effect of time on water-use, 115. 

effect of soil depth on water use, 116. 

effect of soil composition on water 
use, 117, 118. 

effect of, on water use, 120. 

rigor of, and water use, 121. 

effect of cultivation on water use, 121. 

effect of age on water use, 122. 

effect of roots on water use, 122. 

effect of kind on water use, 123. 

effect of seasons on water use, 123. 

water-cost of dry matter, 127. 

carbon assimilation, 128. 

age of, and carbon assimilation, 129. 

conditions of growth, 130. 

water-cost of several plants in differ- 
ent countries, 133, 134. 

range of water-cost, 134. 

effect of soil on water-cost, 137. 

effect of plant-food on water cost, 139. 

effect of cultural operations on water- 
cost, 141. 

vigor of, and water-cost, 143. 

water-cost and varying quantities 
of water, 144. 

nature of, and water-cost, 154. 

development under irrigation, 158. 

response to irrigation, 159. 

proportion of roots, 160. 

proportion of leaves and stems, 163. 

proportion of heads and grain, 166. 

proportion of parts, 169. 

composition, 216. 

water in, 217. 

constituents, 217. 

ash constituents in, 219. 

protein in various, 220. 

fat in, 223. 



492 



INDEX 



Plant, carbohydrates in, 224. 

sugar in, 224. 

woodiness in, 226. 

sugar in, 226. 

color and flavor of, 227. 

cooking value, 228. 

composition of flour, 228. 

tillage and composition, 228. 

use of rainfall in production, 231. 

producing power of rainfall, 232. 

toleration for saline water, 387. 

tolerance for alkali, 392. 

tolerance of various plants for alkali, 
394. 
Plant-food. See also Ash constituents. 

loss by drainage, 78, 79. 

added by water, 87. 

added by river sediments, 101. 

and water used by planting, 118. 

effect on water-cost, 139. 

and alkali, 390. 
Plowing, effect on water use, 120. 
Plow, lateral, 427. 

made first irrigation furrow, 427. 

breaking, 419. 
Plum, protein in, 221. 

sugar in, 225. 
Poplars, 328. 
Potatoes, ash in, 219. 

protein in, 221. 

yield due to rainfall, 234. 

under irrigation, 298. 

duty of water, 344. 

in humid climates, 411. 

early yield, 457. 
Powell, 457, 458, 464, 471. 
Protein, in various plants, 220. 
Prunes, sugar in, 225. 
Puddling, as ditch-lining, 377. 
Pumpkin under irrigation, 307. 

Quantity of water in one irrigation, 23. 
Quince, 314. 

Rainfall. See also Dry-farming. 
annual, 1. 
variations, 2. 
seasonal, 2. 
conservation, 3. 
average, 3. 

use of in crop production, 231. 
irrigation supplementary to, 231. 
crop-producing power, 232. 
crop value in irrigation, 233. 
distribution of, 235. 
conservation of, 235. 
types of, 235. 



Rainfall, storage in soil, 236. 

proportion conserved, 237. 
Raspberries, 326. 

protein in, 221. 

in humid climates, 410. 
Reclamation Act, 460. 
Red River, 96. 
Rees, 230, 329. 

Registers for water measurements, 441. 
Relative humidity, effect on evapora- 
tion, 47. 
Reservoirs, seepage from, 371. 
Response to irrigation, 159. 
Rhine, 84, 97. 
Rhubarb, 310. 
Rice, under irrigation, 262. 
Richman, 188. 
Ridging, tools for, 439. 
Rio Grande River, 91, 96. 
Ripening, delayed by over-irrigation, 

251. 
River water, salinity of, 82. 
Riverside, Cal., 197. 
Roeding, 290, 313. 
Rolling, 62. 
Roman Empire, 449. 
Roosevelt, 462. 
Roots, absorption of water by, 109. 

effect on water use, 122. 

development in spring, 182. 

proportion of, 160. 
Root crops under irrigation, 297. 
Root-hairs, 109. 

Rotation, method of distribution, 361. 
Run-off, 40. 

how to prevent, 41. 
Rye, under irrigation, 255. 
Rye-grass, 278. 

Sacramento, 408. 

Salt Lake City, 78, 455, 470. 

Salt River, 96. 

Sanborn, 187, 188, 468. 

San Joaquin River, 91. 

Saskatchewan River, 84. 

Schantz, 20. 

Schlichter, 405. 

Schultze, 74. 

Season, effect of, on water use, 123. 

time to irrigate short-season crops, 
183. 

dry, 407. 
Second-foot, defined, 331. 

equivalents, 332. 
Sediments, cracked, 68. 

river, composition of, 101. 

physical effect on soil, 102. 



INDEX 



493 



Sediments, cultural treatment of, 103. 

effect on crop yields, 104. 
Seelhorst, 157. 

Seepage. See also Over-irrigation and 
Alkali. 

from Indian canals, 341. 

from reservoirs and canals, 371. 

from over-irrigation, 373. 

arid vs. humid, 375. 

lined with ditches against, 376. 

drainage against, 381. 

economical use of water against, 381. 

and alkali, 384. 
Selina, Ala., 407. 
Sevier River, 375. 
Sewage, value in irrigation, 414. 

use of, 415. 
Shade, effect on evaporation, 47. 
Shad-scale, 397. 
Shantz, 14, 126, 156. 
Shaw, 239. 
Showers, 59. 

Silting, as ditch-lining, 378. 
Slosson, 390. 

Small fruits, under irrigation, 326. 
Smith, 329, 405. 
Smythe, 7, 484. 
Snake River, 91. 
Snow. See also Rain. 

loss by thawing, 41. 
Society under irrigation, 476. 
Soil, size of particles, 9. 

composition, 9. 

surface of particles, 10. 

moisture film of, 11. 

relation of particle and film, 12. 

hygroscopic coefficient, 13. 

wilting coefficient, 14. 

lento-capillary point, 16. 

maximum capillary capacity, 17. 

fill water in, 17. 

as water reservoir, 21. 

capacity for water of different, 22. 

unsaturated under irrigation, 22. 

field capacity of moisture, 29. 

hardpan in, 30. 

gravel in, 34. 

quantity water stored in, 35. 

best for irrigation, 35. 

absorption of water by, 38. 

effect of evaporation, 47. 

self-mulching, 52. 

fertility and cultivation, 59. 

contraction of, 64. 

changes due to water, 64. 

cohesion of particles, 65. 

volume change, 67. 



Soil, cracking of, 68. 

effect of water on top, 69. 

natural packing of, 70. 

successive wetting and drying, 70. 

temperature, 71. 

arid and humid contrasted, 73. 

continuous solubility, 74. 

absorption by, 76. 

composition of drainage water from, 
78. 

depth of arid, 82. 

plant-food added by water, 93. 

washing of, 95. 

seasonal washing of, 98. 

suspended matter added by irrigav 
tion, 100. 

suspended matter from surface, 100, 

composition of river sediment, 101. 

physical effect of sediments, 102. 

cultural treatment of sediments, 103. 

water and soil life, 104. 

effect of sediments on crop yields, 104. 

effect of soil depth on water use, 116. 

effect of composition on water use, 
117, 118. 

effect on water-cost, 137. 

storage of water in, 236. 
Soil fertility and cultivation, 59. 
Soil moisture, 8. 

See also Evaporation, Soil, Water, 
Water-film, and Moisture-film. 

attraction of near bodies, 8. 

film of, 11. 

relation of particle and film, 12. 

hygroscopic coefficient, 13. 

wilting coefficient, 14. 

lento-capillary point, 16. 

maximum capillary capacity, 17. 

free water, 17. 

summary, 19. 

soil as reservoir, 21. 

capacity of different soils, 22. 

unsaturated soils under irrigation, 22. 

movement of, 23. 

distribution of, 25. 

field capacity, 29. 

effect of hardpan, 30. 

distribution in furrow irrigation, 30. 

effect of water table, 34. 

effect of gravel, 34. 

quantity water stored, 35. 

absorption by soils, 38. 

saving by cultivation, 40. 

how disposed of, 40. 

upward movement, 42. 

and evaporation, 43. 

contraction of film, 64. 



494 



INDEX 



Soil moisture, concentration of, 79. 

contrasted with natural waters, 87. 

use of, by plants, 108. 

initial percentage and use by plants, 
111. 

effect of distribution on water use, 
114. 

water-cost of dry matter, 127. 
forghum, alkali-resistant, 396. 

early yield, 457. 
South Africa, 453. 

South America, duty of water in, 342. 
South Dakota, 410. 
Southwestern Colony, 461. 
Sowing wheat, 241, 242. 
Spain, 450. 

duty of water in, 342. 
Spinach under irrigation, 308. 
Spring irrigation, 178. 
Springs, mineral, salinity of, 86. 
Squash under irrigation, 307. 
Sugar beets, 152. 

cultural treatment, 286. 

method of irrigation, 289. 
Stabler, 106. 
Stannard, 444. 
Starch in plants, 226. 
Strawberries, protein in, 221. 
Strawberries, 326. 

sugar in, 225. 

in humid climates, 411. 
Stem, proportion of, 163. 
Stewart, R., 105, 106, 172, 230, 390, 405. 
Stewart, Henry, 484. 
St. Julian Canal, 450. 
St. Lawrence River, 84. 
Storer, 415. 
Storing Water in Soil. See Reservoir, 

Soil and Soil Moisture. 
Sub-surface packer, 62. 
Sub-surface irrigation, 189. 
Sugar beets, time of irrigation, 185. 

ash in, 219. 

protein in, 221. 

time to irrigate, 290. 

quantity of water for, 293. 

duty of water, 344. 

alkali-resistant, 396. 
Sugar-cane, duty of water in Africa, 
339. 

under irrigation, 411. 
Sugar in plants, 224. 
Superintendent for water distribution, 

366. 
Surface irrigation, 193. 
Surveys, water need of, 90. 
Suspended matter. See also Sediments. 



Suspended matter in river water, 95. 

seasonal variation of, 98. 

quantity added to soil, 100. 
Syria, 446. 

Talmage, 405. 

Tannatt, 370, 405. 

Teele, 264, 285, 313, 343, 370, 405, 444. 

Temperature effect on evaporation, 47. 

of soil, 71. 
Tillage is water, 142. 

effect on composition, 228. 

against alkali, 399. 
Time, a factor in water use, 115. 
Time of irrigation, 29, 173. 

at lento-capillary point, 22. 

early spring irrigation, 178. 

winter irrigation, 178. 

irrigation during growth, 182. 

short-season crops, 183. 

long-season crops, 184. 

frequency of irrigation, 185. 

night vs. day irrigation, 187. 

effect on composition, 229. 

wheat, 246. 

for corn, 258. 

of alfalfa, 270. 

of sugar beets, 290. 

for orchards, 319. 
Timothy, 278. 
Tobacco, 310. 
Tollens, 219, 230. 
Tomato, 171. 

under irrigation, 306. 
Tools. See also Machines. 

for irrigation, 419. 
Townsend, 313. 
Transpiration, 110. See also Water-cost. 

water cost of dry matter, 127. 

water of various plants, 133, 134. 

range of ratio, 134. 

effect of seasons, 136. 

ratio, effect of soil on, 137. 

ratio, defined, 131. 
Transvaal, 339. 
True, 405. 
Tucker, 145, 157. 

Union Colony, 460. 

United States, duty of water expres- 
sion, 331. 

Department of Agriculture, 343, 464. 

Bureau of Soils, 78, 395, 401. 

Geological Survey, 442, 457, 464. 

Interior Department, 463. 

Irrigation Investigations, 372, 464. 

Office of Experiment Stations, 383. 



INDEX 



495 



United States Reclamation Service, 
370, 461. 

Utah, alkali from, 391. 

Utah Station, 15, 17, 26, 29, 30, 35, 
38, 48, 60, 77, 88, 111, 126, 129, 
136, 142, 146, 154, 159, 165, 166, 
167, 184, 190, 213, 225, 228, 250, 
255, 259, 292, 294, 336, 468, 469. 
duty of water results, 346. 

Utah, time of irrigation in, 320. 

Valencia Canal, 450. 
Vineland, N. J., 407. 
Von Seelhorst, 145. 
Voorhees, 410, 418, 469. 

Walnuts, spacing, 317. 
Warington, 93. 

Washington, time of irrigation in, 320. 
Water. See also Soil moisture, Rainfall 
and Snow. 

film, 11. 

soil as reservoir, 21. 

how disposed of in soils, 40. 

soil changes due to, 64. 

cracked sediments, 68. 

effect on top soil, 69. 

successive wetting and drying, 70. 

universal solvent, 72. 

continuous solubility of soil, 74. 

composition of drainage, 78. 

river, salinity of, 82. 

composition of river waters, 84. 

river, arid and humid, contrasted, 85. 

lake, salinity of, 86. 

mineral springs, salinity of, 86. 

natural and soil-moisture, contrasted, 
87. 

plant-food added by, 87. 

use of concentrated w. in irrigation, 
89. 

surveys, need of, 90. 

natural composition of, 90, 91. 

natural, classification of, 92. 

plant-food value of, 93. 

river, suspended matter in, 95. 

seasonal variation of suspended mat- 
ter, 98. 

suspended matter from surface soil, 
120. 

suspended matter added to soil by, 
100. 

composition of river sediments, 101. 

and soil life, 104. 

effect of sediments on crop yields, 104. 

absorption by roots, 109. 

tillage is, 142. 



Water, cost and varying quantities of, 
144. 

in plants, 217. 

quantity for wheat, 248. 

storage in soil, 236. 

duty, measurement and division, 331. 

units for measuring, 332. 

measurement of, 347. 

distribution of, 357. 

ground, 374. 

use of saline, 387. 

irrigation, sources of, in humid 
climates, 413. 

conservation methods in humid 
climates, 414. 

constants, 477. 
Water-cost. See also Transpiration. 

of dry matter, 127. 

defined, 131. 

of various plants, 133, 134. 

range of ratio, 134. 

effect of seasons, 136. 

effect of soil on, 137. 

effect of cultural operations in, 141. 

vigor of plant and, 143. 

and varying quantities of water, 144. 

nature of plant and, 154. 

summary of factors, 155. 

of dry matter, 232. 
Water-film, relation to particle, 12. 
Water-logging, drainage against, 381. 
Water master. See also Irrigation 
engineer. 

for water distribution, 367. 
Watermelons under irrigation, 307. 
Waters, 410. 
Water-table, 34. 
Weir, 351. 

rectangular, 351. 

trapezoidal, 352. 

triangular, 352. 

discharge over Cippoletti, 478. 
Welch, 188, 234, 265, 285, 313. 
Westgate, 285. 
Wheat, 152, 168. 

protein in, 221. 

composition of flour from, 228. 

yield due to rainfall, 234. 

spring vs. fall, 241. 

quantity to sow, 241. 

method of sowing, 241, 242. 

method of irrigation, 243. 

cultivation of, 243. 

time of irrigation, 246. 

duty of water, 248. 

yields with varying water, 250. 

possible yields with water, 252. 



496 



INDEX 



Wheat, duty of water, 344. 
early yield, 457. 

Wheelon, 253, 344. 

Whipple, 329, 

Whitney, 48, 63. 

Widtsoe, 7, 20, 39, 63, 106, 126, 133, 
134, 157, 172, 188, 215, 230, 239, 
265, 285, 313, 370, 405, 444, 469. 

Wickson, 215, 313, 323, 329. 

Wilcox, 285, 323, 338, 370, 484. 

Willard, 157. 

Williams, 418. 

Wilson, 345, 370. 

Wilting coefficient, 14. 

Wind, effect on evaporation, 47. 

Wing, 285. 



Winkle, Van, 106. 

Winsor, 356, 370. 

Winter irrigation, 178. 

Wollny, 133. 

Woodiness, in plants, 226. 

Woodward, 405. 

Wright, 405. 

Wyoming, duty of water in, 323. 

Wyoming, alkali from, 391. 

Wyoming Station, 303. 

Yield, effect of sediments on crop, 104. 

Yoder, 418. 

Young, Brigham, 454. 

Young, R. W., 470. 



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